Brake and tcs lights after master cylinder swap

[Jamicord]

After replacing the rotors and pads on the front brakes the brakes felt squishy after being bled multiple times. At that time no lights were on. I put a new master cylinder on and that solved the stopping issue, but right after replacing the master cylinder the brake light and the tcs light came on. I put new abs sensors on the rear wheels and that did not correct it. Every now and then the service 4wd light has started coming on. I scanned the truck and no engine codes were present but a U0401 (invalid data from ecm/pcm) and a C1009 (low brake fluid level) codes were there. The brakes fluid level had been consistent I check it every day. I think I’ll do the front sensors but after that I don’t know what to do. I had one guy recommend bleeding the abs module? Any help or advice anyone can give to give me greatly appreciated!

 

[62Blazer]

Don't take this wrong, but it sounds like you are just randomly replacing parts and hoping you get lucky. Why did you think the rear ABS sensors needed replaced?
If the lights on the dash are on, then there is a code. The problem is that the scanner you are using is not capable of reading the brake module. You need to start with reading the specific codes that are causing the warning lights on the dash and go from there. If the lights came on right after replacing the master cylinder, then most likely it was due with the work you just did. The codes may not even be active, meaning they were set when doing the work but are no longer an actual problem. Just that on some codes even if the issue that caused them to originally set go away, sometimes the codes do not reset until a certain number of key cycles, time, or you clear them with a scanner.

 

[Jamicord]

So would I need to use a specialty scanner of some sort like from a dealership? I have ran it with a couple different scanners, and each one of them told me that the brake fluid was low. The only reason I replaced the sensors is because it was cheap and easy to get to and I had read online that could have been the problem.

 

[Ken226]

So would I need to use a specialty scanner of some sort like from a dealership? I have ran it with a couple different scanners, and each one of them told me that the brake fluid was low. The only reason I replaced the sensors is because it was cheap and easy to get to and I had read online that could have been the problem.

So, you replaced the master cylinder and didn't bleed the brakes? Perhaps the pedal is compressing air in the lines, and your code reader is interpreting that as low fluid.



Pretty much any scanner with bidirectional control will let you access the abs module, read the codes and activate the ABS pumps bleeding procedure. I have a Thinkscan 689BT, Innova 7111 and the trusty ole OBD Link MX/AlfaOBD combo. Any one of those will access the ABS module.

 

[62Blazer]

So would I need to use a specialty scanner of some sort like from a dealership? I have ran it with a couple different scanners, and each one of them told me that the brake fluid was low. The only reason I replaced the sensors is because it was cheap and easy to get to and I had read online that could have been the problem.

You don't need a specialty scanner, just most base model scanners do not read the brake module. This typically includes the scanners most chain auto places use. For example the base level Harbor Freight $39.99 scanners does not read ABS codes, but the $59.99 version does. This is something that should be specified on the product spec sheet when you buy a scanner. There are probably at least a dozen "common" codes that can trigger those lights.
If the brake pedal felt fine prior to installing new rotors and pads, and then suddenly felt off after, I would look at the specific parts and work you just did. It would be quite the coincidence if the master suddenly failed just sitting there. Same thing with wheel speed sensors and such. I know it's part of the brake system but replacing pads and rotors really shouldn't have any affect on the master. If there are no leaks in the system you should also not of gotten any air in the system when doing that work (assuming you didn't take any hoses or anything off....typically don't when doing that level of work).
Did you bench bleed the master before installing?

 

[Jamicord]

I did bench bleed the master cylinder and the whole system after installation. The brakes work great I just can’t seem to get the lights to go off. Is there any way to test the sensor on the master cylinder?

 

[turkeybird56]

You could try the ole disconnect battery cables for at least 1/2 hour than reconnect just remember it could take multiple drive cycles for all the computer modules to talk n synchronize with each other.

 

[Jamicord]

Yes, I have definitely tried this. Unfortunately, the lights still come on!

 

[Ken226]

Yes, I have definitely tried this. Unfortunately, the lights still come on!

I'm not sure how your truck is setup, or which it is closer to, but in the manuals for my 13 Ram, and for the 2011 Durango we no longer own, both diagrams show that the brake fluid level sensor is just a switch.

Could you have damaged the switch, wiring or connector when you were doing the master cylinder swap?

Here is the diagram from the 2011 Durango 5.7 Hemi, which i suspect is probably the same as your 2012 Ram:


And just here is the diagram for my 2013 Ram 5.7:





Both appear to work the same. When the fluid is low, the switch closes to ground. The difference appears to be that in the 2009-2012 the TIPM handles the sensing logic, whereas in 2013+ the BCM handles the sensing function.


In the case of the 2009-2012 trucks, it would be the TIPM rather than the BCM providing the reference voltage, and monitoring the circuit.

If the switch is damaged, or the wiring between the switch and TIPM is shorted to ground somewhere, your low fluid light would be stuck perpetually in ON.

Or, of course, if the diagnostic resistor in the TIPM is bad. That is probably less likely than some wiring or connector getting damaged while you are working on the truck.

 

[Jamicord]

I have checked the wiring and connections and they look good. Is there a way to check if the connections on the master cylinder are working properly, possibly using a multi meter?

 

[Ken226]

I have checked the wiring and connections and they look good. Is there a way to check if the connections on the master cylinder are working properly, possibly using a multi meter?

Probably, but without having one to look at I have no idea how it works or how to test it.

I looked up some pics, but it isn't obvious enough for me to figure out how it works. It kinda looks like a float type switch, but I can't be sure. Any idea?

Have you taken it out to look at it?


Is this it:

https://www.mymoparparts.com/oem-parts/mopar-brake-fluid-level-sensor-68002155aa

 

[Jamicord]

I am going to try jumping the sensor connector to see if that will turn off the lights.

 

[Ken226]

I am going to try jumping the sensor connector to see if that will turn off the lights.

Did you see the wiring diagram above? And the "Theory of operation" from the manual?

Jumping the connector will just pull the circuit to ground and tell the computer that your fluid is low. That's already it's current state, so nothing will change.


You need to test that switch first. If it tests good, then you can check the circuit.

 

[Ken226]

I suspect that it's a float type switch. The reason I say that is because (judging only from the pics) there is no threads, it has to go in a certain way.

Pump out some fluid until the master cylinder is really low, then check continuity across the pins of the switch. Then have someone fill it up while you watch the multimeter and see if/when the switch closes.

While the fluid level is below the level of the switch, is probably a good time to remove it and inspect it. You could even test it while it's out. Check for continuity while it's in it's normal orientation, then test it upside down.

The switch should be closed when low on fluid (installed), and right-side up (removed). The switch should be open when full of fluid (installed) or when upside down (removed).

 

[18CrewDually]

Did you try unplugging the sensor to see if the light goes out?

 

[Ken226]

^^^^^^^^^^

Try that. According to the wiring diagram, unplugging the switch will remove it from the circuit and remove it's ability to pull the circuit to ground.

If it turns off the low fluid light, then that's a pretty solid confirmation of a bad switch.



@Jamicord

 

[Jamicord]

there is no switch that I can see that comes off it is all connected to the master cylinder. I have tried starting it with the plug undone and the lights (TCS and brake) still come on. I put a multi meter on the pins in the master cylinder and the gage didn’t move at all. Does this mean the switch in the master cylinder is bad?

 

[Ken226]

I put a multi meter on the pins in the master cylinder and the gage didn’t move at all.

Your not being very detailed about what you did. I don't know what this means. Gage? What are you calling a multimeter?

You set your multimeter to the resistance setting? With enough fluid removed from the master cylinder that it's level is below the switch? (It's a switch, not a sensor). It showed open, or closed? Then you measured again, with the master cylinder full? Like I said to do in post 14?




First, before messing with the switch again, check the wiring circuit at the harness connector. Set your multimeter to DC volts with the black lead connected to battery ground, and probe both pins. One should be an open circuit, and the other should show battery voltage.

If that tests good, then just replace the switch.





No offense intended, but If you don't know what any the stuff I just just said means, then you should probably take your truck to a shop. Your going to tear it up.

 

[Ken226]

there is no switch that I can see that comes off it is all connected to the master cylinder.

Is this a new switch that came with the new master cylinder, or did you remove the switch from the old master cylinder and install it in the new one?


This is the part youre calling the sensor,, right? The black connector in the middle?

 

[Wild one]

Where did you get the master cylinder from.I wouldn't be surprised if you used an after market / cheap master cylinder,if the switch it comes with,isn't playing nice with your truck.