ABS/TC

Comming second after the Column lock problem, here is some information on the ABS-TC.

This is a new page on the ABS/TC EBTCM DTC codes. Still in development.

Ok you get the 'Service Handling' + 'Service Traction Control' + 'Service ABS' on the DIC. The TC and ABS light are ON on the Instrument Panel. That could be a severe problem or as simple as a bad connection or ground.

First thing is to read the codes to point to the source of the problem.

I had that problem and it took me only a small screw driver to give some ‘spring’ to the female wheel sensor harness connectors. See pictures below.

My friend had the same series of error messages. The dealer told him he had to replace the wheel hub bearing. I took the codes and it was complaining about left wheel sensor. I think that was C1228. I took the ohms with my digital voltmeter and found that the hub was fine. Remove the EBTCM connector and took the ohms at connector. I found that when I was moving the harness at wheel, I was loosing the ohms, therefore, only the 2 feet harness was bad. I switched the 2 feet harness with the other side. And the code switched to the other wheel. He bough a new 2 feet harness and problem was fixed.

An other of my friend got this message on his 2002 Z. Took the codes and that was the steering wheel position sensor. He had it replaced. Every thing is fine since then.

An other of my friends got the same series of messages on his 2001 Z last week. We looked at the codes and it was complaining about the steering wheel sensor. Since it append only once, I told him to live it like that and we will start trouble shooting only if it appends again.

What I want to say, is that each time something with one of the ABS-TC, the car will show all the same message on the DIC, Service Active engine, Service Traction Control, Service ABS. It will illuminate the TC and ABS light on the control panel and disable TC and ABS. You need to read the codes in order to point the source of the problem.

BPMV

Circle in Purple is the Pump or BPMV (Brake Pressure Modulator Valve) and Pump Motor circle in Yellow is the EBTCM Circle in Green is the pump Ground Circle in Blue is the EBTCM connector

Wheel Sensor Connector

Many of us see the ABS and TC light in the control panel and the Service Tranction Control message on the IPC when we hit a bump. That is sometimes caused by the female connector at the wheel sensor. The female connector has like a spring who comes loose. I took a very small screw driver, insert it in the connector and bended the part to make sure the contact would be fine. If the male pin loose contact with the metal in the female hole, the signal will be lost. The female lost the spring effect. This is why I take a small srewdriver and bend the femal metal part to re-gain.

You can see on the picture below the left hole before I fix it and the right one after I fixed it.

Both are fixed on this picture.

Front connector. Wheel side.

Do not forget the Front Connector. Harness side.

Rear Connetor.

This is the EBTCM connector view

Some more ABS-TC information

PCM 1571 H C + 1644 and U1040 HC for the BCM and IPC sometimes when I hit a bump. I cleaned the grounds, PCM, EBTCM connectors. I checked BCM. I was not expecting much change since everything was clean. Went for a test ride and I got the same codes. See update on wheel sensor connector below. (Update April 2006, Since I fixed the wheel sensor connector, I have not got the problem for the past 2000 miles. I do not celebrate yet, but this is a good sign).

PCM 1571. Desired torque is a signal the PCM needs to reduce the engine output torque i.e. reduce the amount of spark advance when the EBTCM detects a wheel slip. When the Desired torque signal is not received by the PCM for 3 seconds from the EBTCM, it stores this code. Since it appends to me when I hit a bump, I plan to check the ORN/BLK wire from Pin 25 on the EBTCM connector to Pin 46 of the Connector 1 of the PCM. And connector C142 close to the Battery.

The B0844 code is set when the PCM cannot get the delivered torque level information from the EBTCM. i.e. (Current PCM DTC P1571 or P1644). The B0844 Disable the ABS system by de-energizing the ABSTRANS relay. And DISPLAY the Service Engine Soon message. The IPC TCS/ABS light is a result of that action. The BCM act as a Police patrol and deactivate the TCS/ABS system when it sees that the PCM has a problem communicating and\or obtaining information on the EBTCM. This is a safety feature. Having said that,The TCS and ABS are not working when you see the TCS/ABS light and the Service Engine Soon message.

It has always been said that the 1571 History code was normal. Is it possible that there is a PCM upgrade for the 97 that make the PCM to delete this code automatically? Let me tell you what I found. I have GMP/97-Y-UPD Engine Controls supplement book. Here is what it says at one of the first page of the book. Then I will go our torque codes. --“This service3 manual supplement is intended to software per campaign 97-040. The Tech 2tm scan tool identifies the current PCM software level of the vehicle you are repairing. If the PCM software is NOT updated, reprogram the PCM as necessary and use the information contained in the supplement to repair the vehicle. This supplement replaces the Engine control Section pages 6-347 through 6-1064 of the Corvette Service Manual (GPM/97-Y-3)”.-- Ok if your books are 98+ you might have that update already. But for us who have the original 3 books, that might be interesting. Some differences: In original book for code 1571: Conditions for SETTING the DTC. -Traction control has not failed -The engine speed is greater than 500 RPM for 20 seconds. -The desired torque signal is not received by the PCM for 3 seconds. In the updated version they added a category. Condition RUNNING the DTC -Traction control has not failed -The engine speed is greater than 500 RPM for 20 seconds. Conditions for SETTING the DTC. -The desired torque signal is not received by the PCM for 3 seconds. But below is what I found interesting. They have changed the conditions for Clearing the MIL\DTC. Condition for Clearing the MIL/DTC: Original version : -A History DTC clears after forty consecutive warm-up cycles, if this or any other emission warm-up cycles, if this or any other emission related diagnostic does not report any failures. -The PCM battery voltage is interrupted. -Use a scan tool in order to clear the MIL/DTC. Condition for Clearing the MIL/DTC: Updated version : -The PCM turns the MIL OFF after three consecutive drive trips that the diagnostic runs and does not fail. -A last test failed (Current DTC) clears when the diagnostic runs and does not fail. This is what I find very interesting. Why they added these 2 conditions for clearing the DTC ? If I understand correctly and this is where I’m not sure I fully understand these 2 condition but to me, it looks like these condition were added to make the DTC go away faster. Let summary, they added 2 ways of clearing the DTC quickly and automatically. If PCM is ok for 3 consecutive drive trips, it removes the DTC. Or last test fails Current DTC Clears when diagnostic runs and does not fail. This is an easy way to fix an harmless and intermittent problem. You just remove the error messages. I have programmer background and know that it can be done. Recap from start. Intermittent 1571 are normal in the 1997. They added 2 conditions to the PCM to clear this intermittent code automatically. They made the same modifications for P1644. Delivered Torque Output. So, having my PCM reprogrammed, I would doubt the previous owner did it, since the column recall is not done, could make the torque DTC to go away. Update. I had the PCM reflashed in February 2006. The 1571 is still there. The difference is that if I reset the code, it does not re-appear until I stop the engine. Before I had the PCM reprogrammed, it was reapearing a few miles after I reset it.