My battery went dead a while back, so I replaced it. Recently the BAS/ESP light went on, and I got the following 8 codes from the ESP module:

C1352 B24/15 Rotary speed and lateral acceleration sensor (over voltage)
C1210 Terminal 30 under voltage
C1035 The signal from N49 (steering angle sensor) is faulty
C1212 Terminal 30 over voltage
C1174 N49 (steering angle sensor) is not initialized
C1142 B34 (ESP brake pressure sensor) plausibility error
C1185 A7/7b1 (BAS diaphragm travel sensor) electrical fault
C1330 A7/7y1 (BAS solenoid valve) electrical fault

I did a search on this site and it seems I need to reset the steering angle sensor, so I did that by turning the steering wheel all the way left and then all the way right a few times. Then I cleared the codes and took the car out for a drive. The surprising thing is that not only the C1035 & C1174 disappeared but the other 6 codes also disappeared and did not come back. My question is if those other codes are related to the steering angle sensor, or can I expect them to reappear after a while.

Thank you.

You need to start monitoring your battery/charging system very close. Bad battery (short in one cell) will make alternator go berserk.

Battery testing for geeks.

For all you geeks out there here is quick look at BM2 battery monitor. Works with Android and iOS. Voltage readout very accurate +/- 0.02V, power consumption 1mA. Stores 30 days of voltage history with sampling rate of two minutes. Here is main interface. CTEK 0.8A battery charger connected.

www.benzworld.org

 

Ah, I see! Thank you Witek. So terminal 30 refers to battery voltage? The battery did go dead after the winter in NY. Son did not replace it right away, so that C1210 under voltage is caused by that, I guess. I replaced the battery with an H8 AGM battery and drove it back to California. Then the voltage regulator goes dead in California resulting in the car shutting down for overvoltage protection, so that's where the C1012 over voltage came from! I had since replaced the voltage regulator in the alternator, but I guess one need to clear the code and reset the steering angle sensor.

Thank you so much for setting my mind at ease about all these mysterious codes.

 

Here is DIN terminal numbering scheme.

DIN 72552 - Wikipedia

en.wikipedia.org

 

Hi Witek,

Thank you for the link. After I cleared the codes they don't come back under normal driving conditions. However, when I braked very hard, the BAS/ESP light is back on and I recovered these two codes.

The first one is from the Electronic Selector Module (ESM) that said P1925 - The braking torque value sent from the traction system via the CAN bus is implausible

The second one is from the Electronic Stability Program (ESP) that said C1142 B34 (ESP brake pressure sensor) plausibility error.

Doe that mean either the ESP sensor under the brake master cylinder or the wiring on the connector are busted?

Thank you.

 

Hi Witek,

Thank you for the link. After I cleared the codes they don't come back under normal driving conditions. However, when I braked very hard, the BAS/ESP light is back on and I recovered these two codes.

The first one is from the Electronic Selector Module (ESM) that said P1925 - The braking torque value sent from the traction system via the CAN bus is implausible

The second one is from the Electronic Stability Program (ESP) that said C1142 B34 (ESP brake pressure sensor) plausibility error.

Doe that mean either the ESP sensor under the brake master cylinder or the wiring on the connector are busted?

Thank you.

Failing harness mimics malfunctioning components. Definitely check the wiring harness first before replacing expensive components. C1140 and P1925 BAS/ESP light on, wiring issue (SOLVED).

 

Thank you Merzatt. I will do a live data on the ESP module while wiggling that connector to see if it's a wiring problem. Then I will report back. By the way, there seems to be only one sensor on the master cylinder. Is that the B34/2 or B34/1, or is it just a B34? Do you happen to have a part number for it, just in case! Thanks again. You and Witek are real lifesavers.

 

There is only one B34 in 2005. Jiggling the wire is not science. You should measure the resistance between the connecter at the ESP module, and the B34 connector. If resistance is <0.5 ohms for all 3 wires, then the harness is good. In my case, one wire was reading 1.2 ohms. PDFs on the link have all the data you need to get rid of the BAS/ESP light.

 

Then the voltage regulator goes dead in California resulting in the car shutting down for overvoltage protection, so that's where the C1012 over voltage came from! I had since replaced the voltage regulator in the alternator, but I guess one need to clear the code and reset the steering angle sensor.

 

Hi Merzatt,

Yes, I will remove the ESP connector and the B34 connector to test continuity in the wiring, since that's the only surefire way to find out. However, I am a little confused about the location of the ESP connector. For your ML500 it seems to be under the washer reservoir, and one might have to remove the reservoir to access that. Is my 2005 ML350 the same, or is it somewhere else?

Thanks

 

1. Remove the driver side wheel well cover
2. Remove the headlight
3. Remove the reservoir bolt to loosen it. You don't need to remove the reservoir. Lift it up gently.
4. Lift the ESP connector locking clip upwards to disconnect it. You can only do this from the front and you will need to push the reservoir up 1-2 inch
5. BPS pins are listed in the PDF on the above link. I removed them from the connector but that is not necessary.

 

It is the same.

 

Hi Merzatt,

Thank you for a very detailed set of instructions. I am in the middle of changing oil, transmission/transfer case/differential fluids, spark plugs, brake flushing ... so it will take a few days before I can get to this. I will come back and provide a detailed report on what I find. The car has 129K miles and had seen 6 winters in Ithaca, NY, so I think it's time to do all that

 

Hi Merzatt,

I finally finished all the other maintenance tasks on this car. I disconnected the ESP connector under the washer reservoir and the pressure sensor connector at the master cylinder to probe the continuity on the 3 points C, D & E (on the PDF document you referenced) with the pressure sensor connector. All 3 of them vacillated between 0.1 & 0.2 Ohms, so they seem to be OK. Do I replace the brake pressure sensor now, or is there other testing to be done? If the sensor needs to be replaced, will 002542841865 be the proper part number?

 

You verified that the harness is good . Now you can do live data check of the BPS values. You can use Autel or DAS . The pressure should go from 0 to higher in a linear fashion with the brake pedal. Do that before ordering the part which is correct number.

 

Hi Merzatt,

OK, I did look at the live data today with the engine running. With my foot off the brake the B34 sensor reads 0. When I stepped on the brake the reading increased pretty steadily until it exceeded 100 bar. I think the ESP/BAS light popped up either at that point or before that, I did not keep an eye on both the instrument panel and the live data. I can turn the key off, then start the car again, and the lights would go away. Any idea what happened there?

Thanks

 

When I tested pressure after fixing the wiring problem, it went up to 50 bar at full pedal pressure. If it sends 100 bar to ESP module, it might be triggering P1925 - The braking torque value sent from the traction system via the CAN bus is implausible. Since your wiring is good, changing BPS might be your next step.

 

Yes, I did get that P1925. You are good! 👍

The other code is a C1142.

 

Yes, I did get that P1925. You are good! 👍

The other code is a C1142.

If the BPS is the culprit, C1142 B34 (ESP brake pressure sensor) plausibility error should go away as well.

 

The last time the BAS/ESP light came on, I went through the history (the Autel has that feature) and it appears that this C1142 fault has happened a dozen times since 86K miles about 8 years ago, and I am at 129K miles now. Also, according to my record, at that time I was flushing the brake with ATE Dot4 SL.6 brake fluid. It seems too coincidental that the problem would start at around the same time I flushed the brake. Did I use the wrong brake fluid?

 

ATE Dot4 is on the approved fluid list and a good one. I am assuming previous owner probably had the same problem.

 

A local shop in my area and Oreilly has the Pentosin Super DOT 4 in 1 liter cans.
Been using it for years as I am impatient and can get it same day.

 

What is Super DOT 4? Is it the same as DOT 4 Plus? I have some VW Super DOT 4. Will that work?

 

DOT 4 plus means DOT 4 with enhancement. There are a lot of fluids that will match MB fluid spec. This is the list at W163 Useful Documents

I ordered MB brake fluid from one of the online MB dealers last month. They said they no longer sell it and canceled the order. Your local dealer may still have it, I didn't ask.

 

OK, final update on what happened. I finally got a genuine MB brake pressure sensor from Pelican Parts. It took a few days to get here. I installed it and tested out with live data. The brand new brake pressure sensor again registered close to 100 bars when I stepped on the brake very hard with the engine on. There is no change to the car's behavior. Whenever I braked very hard, the wheels do not lock up, so the ABS is working. However, without exception, under hard braking the BAS/ESP light goes on with the same two codes P1925 and C1142. Once I turned the engine off and then back on, the BAS/ESP light goes away and the car behaves as if nothing happened.

So my question now is: "Is the car designed that way? Is the BAS/ESP light supposed to light up under hard braking?"

Thanks

 

BAS/ESP light is not supposed to light up under hard braking. Triangle ESP light flashes when ABS is active. Are you sure the wiring harness is good? Is it possible that previous owner replaced the master cylinder with a smaller bore diameter? Or modify to brake pedal travel to increase the brake pressure?

 

Hi Merzatt,

I am as sure as I can be that the wiring harness is good, even though it wouldn't hurt for me to check it again. I am the second owner, and I have no idea what the previous owner did with the car. Did he install a master cylinder with a small bore diameter? Possibly. I was thinking along the same line but had no way to confirm that. I have no idea that one can modify the brake pedal travel to increase the brake pressure. Is the increase due to the travel inside brake booster? Also, the triangle ESP light with the exclamation never came on.

 

I would double check the wiring harness again. MB bulletin dmits that the wiring harness is the weakest link in this design. Symptoms in my car was very similar to yours, and wiring harness was the reason. You can find many YouTube videos about cleaning the ESP plug. Did you use contact cleaner on plugs both ends?

Design weakness of W163 was placing the leaky washer reservoir on top of the ESP/ABS unit with a massive plug. People do a lot of different things to turn that light out. It is possible that a few things were replaced during the previous ownership. Check out the part numbers on master cylinder and brake booster to make sure they fit your car. BAS/ESP issue is a common reason to sell these cars due to high cost.

Brake pressure is generated inside the master cylinder. Length of the break pedal movement directly and diameter of the master cylinder indirectly affects the brake pressure.

ESP triangle turns on while driving on slippery roads. However, it is probable that since there is a fault code in the system, ABS is not being activated by the controller.

 

Had a chance to look at B34. Engine running. Highest I can get is 103 Bar.

 

Hi Witek,

Do you have any errors under hard braking? I am beginning to wonder if the ABS Pump or the ESP module are supposed to regulate brake pressure?

 

No, I do not get any errors. Pressure is developed by master cylinder. ESP module regulates pressures to each wheel but it has no way to control main pressure. All it does is read.

 

DiagnoseDan finds out why ESP module reports Brake pressure sensor fault code, even though there is not wrong with the sensor.

 

DiagnoseDan finds out why ESP module reports Brake pressure sensor fault code, even though there is not wrong with the sensor.

I am subscribed to that channel for a few years. Good stuff.

 

I won't be able to get back to this until early November since we are leaving for Europe for two months. But we will try to get to the bottom of this once I return.