fixbroke

This is cross-posted from LS1Tech, but I haven't had any luck there so I'm hoping the C6 community might have come across something similar with your EBCM. This is in my 2005 CTS-V, which uses the same EBCM as the C6.

I've got an interesting problem that I'm hoping someone here might have some experience with. I've been getting a "service stability system" message in my V for a while, and I finally got my VCX Nano working with Tech2Win so I could read the code and diagnose the problem.

The codes were C0136 (Base Brake System Pressure Circuit) and C0137 (Base Brake System Pressure Circuit Range/Performance), and I was seeing 4.92 volts from the brake pressure sensor.

I unplugged the sensor from the harness and checked the voltage again on Tech2Win, and it was still reading 4.92 volts. Strange! I put a multimeter on the harness connector and sure enough, I had 4.92 volts from both the signal and the +5 reference wire to the low reference wire (with the sensor unplugged), but no continuity between the signal and +5 ref wires.

Looking at the wiring diagram, it seemed that the problem must exist within the EBCM so I pulled it out and had a look. There was evidence of some moisture getting in there, so I thought I had surely found my culprit. I ordered a used one off Ebay and swapped it in, only to find (frustratingly) that the problem persisted.

I've been poring over the wiring diagram to figure out how the signal wire is getting a constant 5 volts when not connected to the sensor, but I'm out of ideas. Does anyone have some guidance on what to look for? Any help would be much appreciated!

Attached are the relevant pages from the wiring diagram. We're looking at wires 11, 12, and 17 (B13, B14, and C10 at the EBCM connector).

It's worth noting that the wire run from the sensor to the EBCM is very short (less than a foot), and I couldn't see any harness damage, so I'm skeptical that the signal wire has shorted to another +5 volt reference.



Wiring diagram pg1

Wiring diagram pg2

C5 Diag

C5 owner here but many sensors on C5,C6's and basically all other cars use a 5 volt reference voltage...MAF,TPS,MAP all have this 5 volt ref. The PCM has a 5 volt regulator within it this sends out this constant voltage to which ever sensor requires it...Here is a good video that will explain it...and that brake pressure sensor is a potentiometer...with another video !!

fixbroke

Thanks rwobs - that all makes perfect sense, but unfortunately it gets me no closer to solving my problem.

The fact that there's no continuity between the signal and +5v wires is the really strange part. I suppose that if there's a diode on either wire that could explain it, but then the short would have to be before the diode in the EBCM, and the replacement of the EBCM should have fixed the issue.

C5 Diag

fixbroke

No continuity = very very high resistance between the wires (OL if reading voltage, many mega ohms if reading resistance). If there was a short between the 5v ref and the signal wire, I would expect to see very little resistance between the two wires (continuity).

To be clear, with the sensor unplugged, either of the 5v ref wire or the signal wire, when checked against the low reference wire, reads ~5v. Across the 5v ref and the signal wires there is 0v.

Thanks for looking into it, rwobs777!

Dano523

O5 CTS,
C0136
Conditions for Setting the DTC
One of the following conditions exists for 0.1 second.

• The brake fluid pressure sensor signal is greater than 4.9 volts.

• The brake fluid pressure sensor signal is less than 0.15 volt.

C0137
Conditions for Setting the DTC
The brake fluid pressure is less than 345 kPa (50 psi) for 3 deceleration cycles.



So lets start with the brake fluid pressure sensor.
pin 1 L-GN/BK 1338 Low Reference
pin 2 PU 5002 Brake Fluid Pressure Sensor Signal
pin 3 GY/BK 1337 5-Volt Reference

Here, the EBCM is going to send 5 volts to the BFP sensor, is going to use the lower reference signal voltage as the base line voltage back at the EBCM from the sensor, and then going to use the fluid pressure sensor signal voltage as the differential reading off the base signal for actual pressure.

Brake fluid pressure sensor may have gone south, or even EBCM, but would bank more of a broken/problem in the above wiring between the connectors for the above problems instead. I bring this up, since GM used very, very small gauge wire for such runs, and it just a mater of time due to such, that the wire ends up breaking inside its own sheilding from even the slightest of movement on the harness looms to start with.

So myself, I just cheat using a test light to begin with. Hence the brake pressure sensor and EBCM connector disconnected, battery cables disconnected from the battery to pull voltage off the other systems, run small gauge wire from the battery positive side to each one of the connectors on the pressure sensor connections one at a time, test light clipped to battery negitive side, then probe the EBCM connector pins to see if there is continuity on the connector to connector female spades in the connectors to light up the test light, or a broke wire or connector pin to wire crimp point problem that is causing the problem to start with.
Note, Pin 1 and pin 2 are direct shots back and forth between the connectors only, but pin 5 reference is used by a couple of other sensor, so this is the reason that I will disconnect the battery from the car when running higher voltage through a 5v referance supply wire. If you want to use a 5v battery source, and 5v test light, will be safe with just pushing 5 volts down the GY/BK wire to test for continually in that wire from the Pressure sensor connector for EBCM to sensor connector instead.

If you find that the one of the wires has a problem, quick way to find the problem is use a tone generator with probe to find the broken wire somewhere in the loom, so know where to spit the loom shielding to do the solder/heat shrink repair to the broken wire to correct the problem.Some time is a easy fix with just the remale spade to wire at the connector having a problem, but lives often not the simple,and you have to start chasing the wire in the loom run to find where the wire is broken isntead.

If the wiring.connector pins are fine between the two connectors, then downloads from GMSI for the two codes on your 05 CVT trouble shooting check lists, as well as connector ends, and your over all diagram of the system since you may need them as well.
http://www.mediafire.com/file/3m0gbc...fu/cvt.7z/file

Note, zipped with 7-zip, and if you don't have decompression program loaded on your machine to unzip the files in the download package, below is the link to download and install 7-zip for free.
https://www.7-zip.org/


If you need something else from GM SI that I did not include on the zip file, let me know.

And to add, with the connector pressure sensor unpluged from the sensor, should have only the 4.9v on the sensor voltage wire with the car in the run postion-motor off, and nothing on on the other two wires with out JL4 (since they are return voltages from the sensor itself). If your getting 4.9v on the low reference wire, or even the pressure signal wire without JL4, then check the wires to make sure that they have not grounded out together someone in the harness before the EBCM.

Look at the PDF for pressure sensor in the download link package, and notice that with JL4 in the car, what you seeing for the voltage is the Steering wheel sensor voltage tapped into these wires isntead.

fixbroke

Thanks for the comprehensive reply, Dano.

I did a test similar to your test light suggestion, where I disconnected the EBCM and the pressure sensor and probed the connector pins on both sides for continuity (I hadn't disconnected the battery, however) and everything checked out perfectly. Do you think it's worth repeating this test as you described?

I also probed for continuity between the signal wire and every other wire on the EBCM connector, but got nothing.

I may try disconnecting the yaw sensor and/or the steering wheel position sensor just to make sure they're not somehow influencing the voltage on the pressure sensor signal.

Dano523

Download this 7-zip file from this below link to start with, and use the 7-zip program to if you don't have a decompression program on your machine. If your running a ad blocker program on the bottom of the page, click download with ad blocker still in use.
Again, all the PDF in the package are from GMSI, and specific to your car and year.

http://www.mediafire.com/file/3m0gbc...fu/cvt.7z/file

Once you have the file unzipped and looking though the PDF files, then we can talk if needed.
In the zipped package download, I included both the GM SI check lists for both codes as well the wiring diagrams for the senors as well (Pressure sensor on the top on the list to so you the see the JL4 tie in).

The Gmsi trouble shooting lists makes trouble shooting a snap to find the problem to begin with!!!!!

Hence looking the Pressure sensor PDF from the above like with both the 136 and 137 code in mind, pretty sure that the problem is one of the wires back to the EBCM is broken/has a bad connection of of it connectors.
Since the steering wheel sensor is not having problems, would bank that the problem is on the Pu wire from the pressure sensor connector to the EBCM connector the problem at hand. Could be an intermediate problem of one of the connector with less that stellar connection of the wire, or the wire snap inside it shielding that is only making contact to it self if the harness is moved into the correct position that is cause the intermittent problem isntead.

fixbroke

Okay, I think this is solved. A new (used) brake fluid pressure sensor gives me a reading of 0 psi. I'll report back once I've bled the system to confirm that it's working as it should when it's pressurized.

I'm still very confused about seeing 5 volts on the signal wire, but if a new sensor fixes the problem then I'm okay with that.

Dano523

Take a look at the PDF that I told you to download, open the pressure sensor PDF once you decompress the file with 7-zip, and you will see that the steering sensor and yaw senor are tied into the same wires (5 volt supply and lower reference) with the JL4 option, and the voltage that your seeing.

Yaw tie in on on the top left of page in the steering wires to the right, and steering sensor is tied in on the right middle of page with the JL4 option in play.

Bexe

fixbroke

Problem solved. The brakes are bled and the sensor is responding to brake pedal pressure.

To reiterate, there is a 5-volt potential between the 5-volt reference and the low reference (as is expected), but there is also a 5-volt potential between the signal wire and the low reference.

Continuity checks were done with the continuity function of the multimeter, checking between the disconnected wiring connectors at the sensor and the EBCM.

0Cicio Performance

Do you have a part number for this switch by chance? I can't find it anywhere....

Thanks
Andrew