Truck went into limp mode with "ETC" warning light - stored P2122

[Wild one]

Thank you for the info but I have a somewhat "less severe" problem. The truck always starts and runs fine but then for no apparent reason all of a sudden goes into limp mode while driving with "lightning bolt", CEL and a P2122 DTC code stored.

If I shut the truck off and re-start it it runs normally again. Then some time later (in this recent case it was 3 months) it happens again.

I took it to the dealer the last time this happened, with DTC stored and CEL still on, but it did no good - they couldn't find anything wrong and just cleared the code.

I don't want to put in a new $$$ computer in unless I'm sure that's the problem.

The problem you described with your truck seems like it could have been a power problem - like it took time for the PCM to "wake up" every time. In my case it seems to be throwing an erroneous code at random.

I fought a similiar issue on my truck,when it only had about 20,000 miles on it,damn near drove me nuts trying to find the issue.I did the same replaced the peddle assembly and throttle body to no avail,finally had my dealer tech buddy come over 1 evening after supper with the dealers scan tool,and we went for a ride,and everytime the truck hit a fairly decent bump,the voltage to the throttle body would drop,and it would go into limp mode.Turned out to be a bad connector pin right at the throttle body,a throttle body electrical repair kit from the dealer and a 1/2 hours time soldering it in place and it's never had another issue since,and that was about 5 years ago.At the time i attributed it to the fact the throttle body had been off and on more times then i could count,but since the fix i've had the throttle body off way more times then before the issue,so i kind of question the quality of the original connector

 

[Racer9]

Did any of this happen before the new battery? It is possible for a bad connection inside the battery. Maybe hook a tester and shake it a bit.

 

[Jebb]

I fought a similiar issue on my truck,when it only had about 20,000 miles on it,damn near drove me nuts trying to find the issue.I did the same replaced the peddle assembly and throttle body to no avail,finally had my dealer tech buddy come over 1 evening after supper with the dealers scan tool,and we went for a ride,and everytime the truck hit a fairly decent bump,the voltage to the throttle body would drop,and it would go into limp mode.Turned out to be a bad connector pin right at the throttle body,a throttle body electrical repair kit from the dealer and a 1/2 hours time soldering it in place and it's never had another issue since,and that was about 5 years ago.At the time i attributed it to the fact the throttle body had been off and on more times then i could count,but since the fix i've had the throttle body off way more times then before the issue,so i kind of question the quality of the original connector

Thank you for that input. It very well could be a bad wire or connector somewhere but the dealership supposed checked and couldn't find anything wrong. It has run fine for 3 months (~1000 miles) since the last time it happened so trying to find the issue test driving is gonna be tough.

Every time it has failed it has done so while idling in Drive and coming up to, or stopped, at an intersection. I'm wondering if it's something in the throttle body (sticking throttle plate at idle?) and will check it today.

 

[Jebb]

Did any of this happen before the new battery? It is possible for a bad connection inside the battery. Maybe hook a tester and shake it a bit.

Good question - NO, this did not happen before the new battery. Before the new battery was installed the truck was jump-started. After the new battery was installed there was a CEL and a bunch of stored DTCs. I asked the dealership about it and they said that DTCs after a jump start and battery swap was normal but I'm not 100% convinced. However all the DTCs eventually cleared on their own and the truck runs normally MOST of the time. I would think that if jump starting fried anything the truck would not run at all.

If the battery was bad would the truck crank/start so easily? I did check the battery connections awhile back and everything seemed good. No corrosion, nothing loose, etc.

But I will look into this. Thank you for the suggestion.

 

[Black-Wolf]

Based on what I'm reading here:

1) You have replaced your pedal with a new one
2) you do NOT have a pedal commander or other throttle control accessory
3) The dealer is unable to replicate the problem, and has not been able to provide a reason why (no surprise)
4) This started happening after you vacuumed the truck once a while ago, and has been intermittent since.

All of this usually indicates either a lose pin or wires broken inside the pin (so that the wire winds up only having a few strands actually connected inside the pin - all the others are connected intermittently at the break, but when too many are not, it causes the voltage passed by the wire to be lower than it should - i.e.: out of tolerance) to the pedal or the TBC, a lose or dirty connector (causing lower voltage on that channel), a bent or lose pin, or a wire that is shorting out to ground in the harness (it happens - usually when a wire rubs regularly against something sharp).

The Pedal gets +5VDC in on two channels, and sends out put through two resistor channels: as you press the pedal, less resistance means more voltage is sent to the PCM.

Both channels should be the same (within a few mV) voltage of each other.

If one channel is out of tolerance from the other, it triggers the DTC, and puts you into limp mode - mainly to protect you from a faulty pedal causing unintended acceleration - which could of course cause you to wreck.

If the internals of the pedal are bad, or one of the resistance channels is failed or failing, the voltage across that channel will be much lower than the channel that is working - again, this causes an "out of tolerance" situation, and you get put into limp mode - throwing one of the 21xx codes usually.

Since the pedal is the only part that moves in this circuit (your code will throw before the throttle side of this is involved because the PCM will detect the error before it sends output to the throttle) this is the most likely failure locations.

Since you've replaced the pedal, the next part would be any connectors that are in the circuit - the closer a connector is to a moving part, the more likely it is that it could have premature failure - leading to the wires where they connect to the pins, the pins themselves (bent, broken internally, or lose - the pin MIGHT look fine, but it could be bad - and you'd not know it), or the connectors not seating correctly.

Check for +5 VDC at each of the supply side pins, and verify you have good ground on both ground pins. The signal pins will be more difficult to determine if there's a problem, but I believe you can use AlphaOBD to monitor the output through the PCM.

I've attached the wiring diagram for the circuit in case you need it. The pedal side is exactly the same across all models with possible exception of the pin numbers on the PCM/Firewall.

 

[MJP81]

After reading all this, i would be inclined to warranty that battery out and put in a new one....but another thing to check: I had an intermittent issue with my last truck (a chevy...) that was turning my traction control on and off and throwing a bunch of codes. replaced a bunch of sensors, still issues. Then I read about electrical fretting corrosion. basically, the pins on electrical plug connectors get "corroded" I couldn't see any corrosion, but it was there, because i took a tiny piece of scotch brite pad, took apart my connections on the sensors I thought were causing the issue, and rubbed down all those pins the best I could with the pad. put a little dielectric grease on everything, put it back together, and never had another problem. Not sure if it'll solve your issue, but at this point, maybe worth a shot?

 

[Jebb]

Based on what I'm reading here:

1) You have replaced your pedal with a new one
2) you do NOT have a pedal commander or other throttle control accessory
3) The dealer is unable to replicate the problem, and has not been able to provide a reason why (no surprise)
4) This started happening after you vacuumed the truck once a while ago, and has been intermittent since.

All of this usually indicates either a lose pin or wires broken inside the pin (so that the wire winds up only having a few strands actually connected inside the pin - all the others are connected intermittently at the break, but when too many are not, it causes the voltage passed by the wire to be lower than it should - i.e.: out of tolerance) to the pedal or the TBC, a lose or dirty connector (causing lower voltage on that channel), a bent or lose pin, or a wire that is shorting out to ground in the harness (it happens - usually when a wire rubs regularly against something sharp).

The Pedal gets +5VDC in on two channels, and sends out put through two resistor channels: as you press the pedal, less resistance means more voltage is sent to the PCM.

Both channels should be the same (within a few mV) voltage of each other.

If one channel is out of tolerance from the other, it triggers the DTC, and puts you into limp mode - mainly to protect you from a faulty pedal causing unintended acceleration - which could of course cause you to wreck.

If the internals of the pedal are bad, or one of the resistance channels is failed or failing, the voltage across that channel will be much lower than the channel that is working - again, this causes an "out of tolerance" situation, and you get put into limp mode - throwing one of the 21xx codes usually.

Since the pedal is the only part that moves in this circuit (your code will throw before the throttle side of this is involved because the PCM will detect the error before it sends output to the throttle) this is the most likely failure locations.

Since you've replaced the pedal, the next part would be any connectors that are in the circuit - the closer a connector is to a moving part, the more likely it is that it could have premature failure - leading to the wires where they connect to the pins, the pins themselves (bent, broken internally, or lose - the pin MIGHT look fine, but it could be bad - and you'd not know it), or the connectors not seating correctly.

Check for +5 VDC at each of the supply side pins, and verify you have good ground on both ground pins. The signal pins will be more difficult to determine if there's a problem, but I believe you can use AlphaOBD to monitor the output through the PCM.

I've attached the wiring diagram for the circuit in case you need it. The pedal side is exactly the same across all models with possible exception of the pin numbers on the PCM/Firewall.

Thank you for the info. My next question was going to be if anyone knew where I could find the wiring diagram! Thank you.

Actually, in reading back through my own posts as well as the recent one above, this all started happening after the battery was replaced. The battery was replaced immediately following a jump start which threw a bunch of DTCs.

Anyhow, I will check all of what you suggested. Thank you.

 

[Jebb]

After reading all this, i would be inclined to warranty that battery out and put in a new one....but another thing to check: I had an intermittent issue with my last truck (a chevy...) that was turning my traction control on and off and throwing a bunch of codes. replaced a bunch of sensors, still issues. Then I read about electrical fretting corrosion. basically, the pins on electrical plug connectors get "corroded" I couldn't see any corrosion, but it was there, because i took a tiny piece of scotch brite pad, took apart my connections on the sensors I thought were causing the issue, and rubbed down all those pins the best I could with the pad. put a little dielectric grease on everything, put it back together, and never had another problem. Not sure if it'll solve your issue, but at this point, maybe worth a shot?

Will take a look. Thank you.

 

[Black-Wolf]

The battery was replaced immediately following a jump start which threw a bunch of DTCs.

If the battery was replaced, there is a possibility you need to recalibrate the pedal - I'm don't know if that applies to the 1500 series - I haven't had to do that - but I believe it applies to older 2500 diesel models...

 

[Jebb]

If the battery was replaced, there is a possibility you need to recalibrate the pedal - I'm don't know if that applies to the 1500 series - I haven't had to do that - but I believe it applies to older 2500 diesel models...

I don't know if it applies either but I already did it anyway and the problem happened again since.

 

[Jebb]

Based on what I'm reading here:

1) You have replaced your pedal with a new one
2) you do NOT have a pedal commander or other throttle control accessory
3) The dealer is unable to replicate the problem, and has not been able to provide a reason why (no surprise)
4) This started happening after you vacuumed the truck once a while ago, and has been intermittent since.

All of this usually indicates either a lose pin or wires broken inside the pin (so that the wire winds up only having a few strands actually connected inside the pin - all the others are connected intermittently at the break, but when too many are not, it causes the voltage passed by the wire to be lower than it should - i.e.: out of tolerance) to the pedal or the TBC, a lose or dirty connector (causing lower voltage on that channel), a bent or lose pin, or a wire that is shorting out to ground in the harness (it happens - usually when a wire rubs regularly against something sharp).

The Pedal gets +5VDC in on two channels, and sends out put through two resistor channels: as you press the pedal, less resistance means more voltage is sent to the PCM.

Both channels should be the same (within a few mV) voltage of each other.

If one channel is out of tolerance from the other, it triggers the DTC, and puts you into limp mode - mainly to protect you from a faulty pedal causing unintended acceleration - which could of course cause you to wreck.

If the internals of the pedal are bad, or one of the resistance channels is failed or failing, the voltage across that channel will be much lower than the channel that is working - again, this causes an "out of tolerance" situation, and you get put into limp mode - throwing one of the 21xx codes usually.

Since the pedal is the only part that moves in this circuit (your code will throw before the throttle side of this is involved because the PCM will detect the error before it sends output to the throttle) this is the most likely failure locations.

Since you've replaced the pedal, the next part would be any connectors that are in the circuit - the closer a connector is to a moving part, the more likely it is that it could have premature failure - leading to the wires where they connect to the pins, the pins themselves (bent, broken internally, or lose - the pin MIGHT look fine, but it could be bad - and you'd not know it), or the connectors not seating correctly.

Check for +5 VDC at each of the supply side pins, and verify you have good ground on both ground pins. The signal pins will be more difficult to determine if there's a problem, but I believe you can use AlphaOBD to monitor the output through the PCM.

I've attached the wiring diagram for the circuit in case you need it. The pedal side is exactly the same across all models with possible exception of the pin numbers on the PCM/Firewall.

Now this is just getting weird. Today I climbed in the truck and, as usual, it started right up. But this time there were NO warning lights - no CEL, no lightning bolt - and it ran completely normally ALL DAY.

I had not cleared the DTC codes and I had only driven about 8 miles since this recent "limp mode" episode. I checked and it still shows P2122 and U1428 are stored - so why did the CEL go off all by itself?

I've run checks on the battery and alternator and inspected the APPS connectors and everything is good. Voltages and continuity at the pins of APPS and harness all check out.

So what's going on here? AFAIK, the "CEL" will only self-clear after 50 miles with no repeat occurrence of the problem - so why is it off NOW after only ~8miles? I'm starting to think it's the PCM. Maybe these aren't even real DTCs?

 

[Jebb]

Hi All,

I thought after the last episode that MAYBE it had finally cleared - but I was wrong. Truck went into LIMP mode again today while driving with the same "Service ETC" lightning bolt and CEL. Scanner shows same code again, P2122. I already replaced the Throttle Pedal Assembly and that did not fix it.

It has been 4 months since the last time it did this. I have searched and found nothing wrong - 2 times the dealership searched and found nothing wrong. The last time they kept it for 2 weeks. With this much time between episodes how can this ever be diagnosed? I can't leave it at the dealership for 4 months and he's not going to drive it around with a scan tool attached for 4 months - so what can I do?

Dealer suggested to start replacing parts - at my cost (it's now out of warranty) - but that will be a guessing game since it could be several months before the issue shows up again, i.e., "it's fixed - on no, wait, it isn't, etc., etc.".

Any other suggestions? This has been going on for a couple of years now. What would you do at this point?

 

[Black-Wolf]

Take a look at the video link below. It might help you figure out the cause. Based on the intermittent nature of your issue, I'd say it's a bad wire or lose connection - probably being affected by temperature. On my own personal side note: When my truck threw the P2122 code, my Pedal Commander was actually working its way lose on the pedal side of the harness... because the locking tab was broken off. PC repaired it for $30, and I haven't had an issue since (knocking on some fake wood here). Back to your issue: I'd check for loose/broken connectors, and take a good hard look at how the wires are routed under the dash - make sure that they can't "accidentally" be either kicked or snagged.

See if this helps/gives you any ideas: https://www.youtube.com/watch?v=tfonUJSIjGM

 

[Vik57hemi]

Hi All,

I thought after the last episode that MAYBE it had finally cleared - but I was wrong. Truck went into LIMP mode again today while driving with the same "Service ETC" lightning bolt and CEL. Scanner shows same code again, P2122. I already replaced the Throttle Pedal Assembly and that did not fix it.

It has been 4 months since the last time it did this. I have searched and found nothing wrong - 2 times the dealership searched and found nothing wrong. The last time they kept it for 2 weeks. With this much time between episodes how can this ever be diagnosed? I can't leave it at the dealership for 4 months and he's not going to drive it around with a scan tool attached for 4 months - so what can I do?

Dealer suggested to start replacing parts - at my cost (it's now out of warranty) - but that will be a guessing game since it could be several months before the issue shows up again, i.e., "it's fixed - on no, wait, it isn't, etc., etc.".

Any other suggestions? This has been going on for a couple of years now. What would you do at this point?

Hey did you ever figure out the issue ?

 

[Jebb]

Hey did you ever figure out the issue ?

Nope. Replaced the Accel Pedal Assembly; checked the connectors; wires, etc., and - so far - have found nothing wrong. Whatever it is is not obvious and happens so infrequently that taking it to the shop has been fruitless as well (always works perfectly for the repair man). The only things I can think of that happened around the time this problem first started was 1) battery went dead and was replaced and 2) I installed LED high beam headlights. I don't think headlights have anything to do with this BUT confused signals on the CAN BUS and/or a bad battery can cause all kinds of weird issues, so... But I hate to start replacing more stuff if it's NOT the problem. Dealer is guessing as well. Said his next step would be to start replacing harness assemblies (big buck guessing at my expense).

 

[Ken226]

Do you have a wiring diagram and checked the integrity of the circuits involved with a multimeter?

Does it happen often enough that you could monitor live data pids with a scan tool while a buddy drives you around? See if you can figure out which circuit is suffering the voltage drop?

A common issue that is really difficult to diagnose is loose pins inside connectors.

Is Your Mercedes Connector Wired Correctly? Check This Now

Mike here, with an electrical diagnostic tip focusing on a Mercedes-Benz connector that had a broken wire from a previous car repair. This do it yourself gui...

youtu.be

When an engine is idling, it tends to vibrate a little more. It also moves a lot torsionally, when accelerating and when engine braking, so bad connections and wiring issues tend to manifest under those conditions more than when under constant speed.

Dodge/Chrysler p2122 ITS NOT THE PEDAL!

Enjoy the videos and music you love, upload original content, and share it all with friends, family, and the world on YouTube.

youtu.be

At the 26 min point, you can see his app1 and app2 voltage, to compare to your own if/when it drops out while testing.

 

[Jebb]

Do you have a wiring diagram and checked the integrity of the circuits involved with a multimeter?

Does it happen often enough that you could monitor live data pids with a scan tool while a buddy drives you around? See if you can figure out which circuit is suffering the voltage drop?

A common issue that is really difficult to diagnose is loose pins inside connectors.

Is Your Mercedes Connector Wired Correctly? Check This Now

Mike here, with an electrical diagnostic tip focusing on a Mercedes-Benz connector that had a broken wire from a previous car repair. This do it yourself gui...

youtu.be

When an engine is idling, it tends to vibrate a little more. It also moves a lot torsionally, when accelerating and when engine braking, so bad connections and wiring issues tend to manifest under those conditions more than when under constant speed.

Dodge/Chrysler p2122 ITS NOT THE PEDAL!

Enjoy the videos and music you love, upload original content, and share it all with friends, family, and the world on YouTube.

youtu.be

At the 26 min point, you can see his app1 and app2 voltage, to compare to your own if/when it drops out while testing.

Thank you for the info and suggestions. It only happens about 2-3 times a year so I would have to drive around with the scan tool connected for months - but maybe that's what I'm going to have to do. Dealer mechanic had it for two weeks and found nothing. Said he wiggled wires and connectors with engine running and it had no effect/no codes tripped. When it DOES happen it stores P2122 and U1428.

I will take a look at the videos. Thank you.

 

[Ken226]

Thank you for the info and suggestions. It only happens about 2-3 times a year so I would have to drive around with the scan tool connected for months - but maybe that's what I'm going to have to do. Dealer mechanic had it for two weeks and found nothing. Said he wiggled wires and connectors with engine running and it had no effect/no codes tripped. When it DOES happen it stores P2122 and U1428.

I will take a look at the videos. Thank you.

Check the freeze frame data for the code.

Do you have a scan tool? Anyone who wants to do their own maintenance and repairs on a modern car HAS to have one. And not some 20$ price of ****. Something that actually works.



A commonly used feature of a bidirectional scan tool is called "freeze frame data". It's very useful for diagnosing intermittent faults.

In your case, I'd be wanting to see this APP voltages @ the moment the mil light illuminated.

Reading Freeze Frame Data

This video will outline how to read Freeze Frame data with BlueDriver. Freeze Frame provides a snap shot of the state of your vehicle the moment your check e...

youtu.be

For example, on my Thinkscan 689bt when you click on the trouble code, the next menu gives the option for "read freeze frame (mode 02)".

The manufacturer of your truck decides which pids to make available to the scan tool, so they may not all be there. Or, maybe they are, I'd have to get the same code and scan it to know, but APP is probably there.

 

[Jebb]

@Ken226 - yes, I have a scan tool. It's a Zurich 13s (that I just found out has been discontinued ). Anyhow, it captures and stores freeze frame. I read it one time after getting the DTC and it showed a low voltage on "APP sig 2" - which is basically what the DTC says so it didn't help much. Checked it after clearing the DTC and driving for a bit and it showed everything normal. Because this problem is so intermittent I don't have a clue how to track it down. Could be a harness, connector, bad ground, bad battery, CAN BUS noise or even the PCM/TCM.

 

[Ken226]

it showed a low voltage on "APP sig 2" - which is basically what the DTC says so it didn't help much.

It helps a lot. You've narrowed down the number of circuits that need tested to 1. Which, while significantly more problematic than zero, is still way fewer than the number of circuits that you'd have had to test without this info.

I don't have a clue how to track it down.

Since you know which circuit, you unplug both ends. You check continuity between it and ground while wiggle testing it and look for a short to ground.

Then, you load test the circuit with a test light, wiggle it and watch for the light to drop out.

Then drag test the pins inside the connector at each end of the circuit.

For each of these tests, there are countless videos on YouTube, not to mention the ones I've already linked.

Could be a harness

Yes, see above

, connector,

Yes, see above

bad ground

No. Bad ground = lost communication and/or circuit high codes

, bad battery

Test, replace if needed.

CAN BUS noise

No. This results in Lost communication with xx or yy

or even the PCM/TCM.

When you've done the work and tested everything else, not guessed, but physically tested and verified, and those variables are factored out, if the PCM is only thing left, then you can consider that. But, the PCM gets info from that sensor by reading the voltage, so it stands to reason that since it's giving a low voltage code, that it does in-fact appear to know how much voltage is on that circuit.



It's not going to be solved on the forum. The forum is only going to point you to the right place to start the work of testing and diagnosing. You're gonna have to buy tools, buy test equipment then do manual labor.

Or pay someone else to do it.