Nightmare P2138

[Spanishyeti13]

Hello,

2015 Ram 1500 3.6 4wd
237,000km
New battery Jan 2026
Alternator 2022

I need help with a P2138 code that's getting the best of me.

For about a year I have had a very infrequent (every other month) P2138 code, service etc and the truck would rev to 2000rpm. I would be able to clear the code or even turnt the truck off the back on and it would disappear.

A few weeks ago it has got worse, i got stranded with it not beign able to clear for about an hour. Thats when i did some research and changed the accelerator pedal.
That did not seem to solve the problem.

Up until last weekend it would only happen once. Now the code is stuck on and instantly flashes service etc and revs to 2000, It does idle if I put my foot on the brake though.

I spent some time making sure all my connections at the pcm pedal and throttle body are ok and all my voltage test are seemingly good from what im able to live read with alfaOBD. I took the plenum off and looked all along my wire harness in search of corrosion but cant find any. I overlay some wires from the pedal to the pcm to see if one of my signal wires was bad but no difference.

At the moment from reading of similar cases I think im looking at a bad PCM or throttle body?

Any help would be greatly appreciated

Thank you

 

[RamDiver]

Hello,

2015 Ram 1500 3.6 4wd
237,000km
New battery Jan 2026
Alternator 2022

I need help with a P2138 code that's getting the best of me.

For about a year I have had a very infrequent (every other month) P2138 code, service etc and the truck would rev to 2000rpm. I would be able to clear the code or even turnt the truck off the back on and it would disappear.

A few weeks ago it has got worse, i got stranded with it not beign able to clear for about an hour. Thats when i did some research and changed the accelerator pedal.
That did not seem to solve the problem.

Up until last weekend it would only happen once. Now the code is stuck on and instantly flashes service etc and revs to 2000, It does idle if I put my foot on the brake though.

I spent some time making sure all my connections at the pcm pedal and throttle body are ok and all my voltage test are seemingly good from what im able to live read with alfaOBD. I took the plenum off and looked all along my wire harness in search of corrosion but cant find any. I overlay some wires from the pedal to the pcm to see if one of my signal wires was bad but no difference.

At the moment from reading of similar cases I think im looking at a bad PCM or throttle body?

Any help would be greatly appreciated

Thank you

Given the vintage of your truck, I would be carefully examining all the wiring and connectors between the accelerator pedal and the PCM. Take extra care with illumination to see any oxidation or displaced connector pins. I like using LED lighting for these tasks.

Also, a very careful examination, visually & electrically, of all B+ and ground wires in this specific area, A-pedal to PCM. Don't forget any common grounds used in this area.

Be sure to refubish any ground connections to the chassis, if any are used in this area, because a visual inspection may not show the problem.

Do you have a digital multimeter, and do you have experience verifying connectivity using the ohm meter?

This link has a few good tips.

P2138 DTC Throttle/Pedal Pos Sensor/Switch D / E Voltage Correlation

The 2013-2016 Service manual may help. Download the PDF to a PC and use 'Control F' to word search.

Pdf service manual

Has anyone found a 4th generation service manual in a PDF format? If so can you please share the link? I can't get the McFall one to work on my phone. Thanks!

www.ramforum.com

And welcome to Ram Forum.

.

 

[Spanishyeti13]

Given the vintage of your truck, I would be carefully examining all the wiring and connectors between the accelerator pedal and the PCM. Take extra care with illumination to see any oxidation or displaced connector pins. I like using LED lighting for these tasks.

Also, very careful examination visually & electrically of all B+ and ground wires in this specific area, A-pedal to PCM. Don't forget any common grounds used in this area.

Be sure to refubish any ground connections to the chassis, if any are used in this area, because a visual inspection may not show the problem.

Do you have a digital multimeter, and do you have experience verifying connectivity using the ohm meter?

This link has a few good tips.

P2138 DTC Throttle/Pedal Pos Sensor/Switch D / E Voltage Correlation

The 2013-2016 Service manual may help. Download the PDF to a PC and use 'Control F' to word search.

Pdf service manual

Has anyone found a 4th generation service manual in a PDF format? If so can you please share the link? I can't get the McFall one to work on my phone. Thanks!

www.ramforum.com

And welcome to Ram Forum.

.

I appreciate the info, I will check it out. Ill try and look over the grounding. Im good with a multimeter, in some cases voltage wont tell you everything, any good way to load test these small wires?

 

[RamDiver]

I also forgot to ask, is anything in this area modified?
Like an accelerator controller?

.

 

[Spanishyeti13]

I also forgot to ask, is anything in this area modified?
Like an accelerator controller?

.

Bone stock, im trying to avoid taking it to a dealer. I can get a throttle body for about 200$CAD and a programed pcm from flagship one for 450$ CAD. I dont like throwing parts at it without knowing what it is exactly but this is my only vehichle now as I sold my jeep not too long ago.

 

[Wild one]

By chance did you have the throttle body off or disconnected ,if so check the pins inside the connector over close for corrosion and make sure none are bent or pushed back.

 

[Spanishyeti13]

Only disconnected

By chance did you have the throttle body off or disconnected ,if so check the pins inside the connector over close for corrosion and make sure none are bent or pushed back.

I have only disconnected the wire harness, I checked it out but I'll try and get a better look at the pins and female connectors tomorrow.

 

[Wild one]

Only disconnected

I have only disconnected the wire harness, I checked it out but I'll try and get a better look at the pins and female connectors tomorrow.

I fought that code for quite awhile,turned out to be a bad throttle body connector,$50 bucks later and an hour or so of soldering in a repair throttle body harness,that i picked up at the local dealer,and i never had another issue

 

[RamDiver]

I appreciate the info, I will check it out. Ill try and look over the grounding. Im good with a multimeter, in some cases voltage wont tell you everything, any good way to load test these small wires?

Unfortunately, measuring a low resistance with a multimeter isn't that precise.
Results will be primarily limited to an open or closed circuit.

Conductivity through a wire will appear as .2 ohms (+/-) for a closed circuit or infinity if open.

A micro-ohm meter isn't cheap or available at Walmart or Harbour Freight.

If you can get a set of mini test clips for the multimeter, it will be much easier to test the individual wires.

Test clips will help to identify poor or flaky conductivity by allowing hands free connection of the multimeter to both ends of a wire, leaving your hands available to carefully flex the harness.

I will get a picture of these test clips tomorrow and post them for reference.

These wires and circuits operate at a relatively low current and without knowing the precise micro-ohm value, calculating a voltage drop would be impractical.

I would first focus on a visual inspection of all connectors in the circuits in question and any associated grounds and B+ integrity.

And any chassis ground connections.

.

 

[Spanishyeti13]

Update from tonight

I put an new throttle body from dormant in, preformed the re-learn through Alfaobd, no change same code...

The code has been stuck on for a week now, I took it for a test drive around the block see if the pcm just needed some time with the new throttle body.

Examined the wires again and preformed continuity checks from the APPS to the pcm and from the TPS to the pcm. Good readings on all the wires so I know I dont have a dead short at least.

No idea still what it could be.

Put everything back together to run some tests with the engine running....Truck wont turn over now, great

I now have some new codes as well
P2111 Throttle Acuator Control Stuck Open

P0222 Throttle/Pedal Position Sensor/Switch B Circuit

P0123 Throttle/Pedal Position Sensor A Circuit High

Im at the end of my rope with this one. Might need to take it to a shop unfortunately

 

[Hemi395]

P2138 has to do with the accelerator pedal, have you checked the connections at the pedal itself?

 

[Spanishyeti13]

P2138 has to do with the accelerator pedal, have you checked the connections at the pedal itself?

I have not officially checked the pins at the pedal because I put a brand new one in which didn't fix the problem. I can see the sensor working through alfaobd though

 

[Spanishyeti13]

Working on it today I have the following codes now

Went to check for 5v (koeo) off the throttle body connector 0v, went to check at the connector before the pcm and 0v as well

Checked all my connectors in C1 and C2 at the pcm no corrosion no bent pins, continuity still checks out but no V

 

[Ken226]

Working on it today I have the following codes now View attachment 583954

Went to check for 5v (koeo) off the throttle body connector 0v, went to check at the connector before the pcm and 0v as well

Checked all my connectors in C1 and C2 at the pcm no corrosion no bent pins, continuity still checks out but no V

Before condemning the PCM, look at a wiring diagram and figure out which sensors share that 5v power feed. All of them.

Then unplug them and retest, one at a time. Unplug, test, plug back in and move to the next.


Any one of the sensors on that same 5v power feed that shorts to ground will pull the entire circuit down, then none of the sensors on the circuit will have a 5v reference signal.

All due to one sensor failing in a short to ground mode.

 

[Spanishyeti13]

Thanks for the reply,
I have the wiring diagram so I'll check for short on all the sensors next

 

[Spanishyeti13]

Saving the oil pressure sensor for last, changed that on my jeep and it was a pita to get to

 

[04fxdwgi]

This is where a nice / decent scantool would come in kinda handy. You can even rent one on ebay.

AlfaOBD is a great program, but not a replacement for a scan tool.

 

[RamDiver]

I have not officially checked the pins at the pedal because I put a brand new one in which didn't fix the problem. I can see the sensor working through alfaobd though

Keep in mind, when you get through correcting the 5V reference signals, that the wiring and connector at the accelerator pedal are on the high suspect list and should be verified.
Unless another fault is identified and the resulting corrective action remedies the deficiencies.

AlfaOBD may be able to see the sensor at the A-pedal, but it has almost zero ability to confirm the integrity of the ground and B+ line.

Compromised grounds and B+ signals tend to be a complete crap shoot with the impact on digital electronics. Proper verification is just a smart idea and could save lots of wasted time.

.

 

[DC Tradesman]

With the age of the truck. The best shot gun method is test/replace the most commonly used part.
Gas pedal/body. I would suspect a worn out unit.

 

[dopey137]

I have a 2014 3.6 - went through the same things with throttle body voltage- I could not find a wiring issue either - but the sensors on the oil housing are on the same 5 volt bus - I change the entire oil housing and sensors at the same time since the plastic housing is know to leak and the wiring is also know to frey at the sensor connection. . While I had it apart - also changed the spark plugs. My issues went away after that. I opted for a new all metal oil housing - was almost the same price as the plastic one. Hope this helps..