I'm getting several codes, P1571, B0844, which I believe are all related to the TCS NO COM. Anyone know which ground the TCS goes to? Where is the TCS module located? Any other suggestions?

Thanks,
Richard

 

The TCS is actually the EBCTM - located in the engine compartment, forward of the driver, there are two modules screwed together ... the EBCM which has wiring going to it, and the BPMV which is the pump and has brake lines coming out of it to each wheel.

The EBCM gets power through three fuses

Fuse 52 (40 Amp) in the engine compartment fuse block
Fuse 5 (10 Amp) " " " " " "
Fuse 8 (20 Amp) in the Instrument Panel Fuse Block (controls brake lights)

It is grounded at two locations - G103 and G108

See Bill Curlee's sticky at the top of the TECH section on wiring to see where these grounds are.

 

Thanks much. Can't seem to locate G108, I see its "G108: Electronic brake control module", but where is it located, or is it the module itself?
thanks again

 

G108 is the ground for the EBCM electronics. G101 on 2000 and older cars is the ground for the pump motor which gets its voltage from the EBCM. G103 is the pump ground for 2001 and newer cars. I just posted some pictures in this thread:

http://forums.corvetteforum.com/show....php?t=1859381

However, why not state what is happening. As far as I can tell there is no code B0844. What year car are we talking about? Are you getting a NO COMM on the TCS? P1571 sets if the PCM doesn't see a requested torque signal from the EBCM or the PCM detects an error in itself. If you have any other PCM codes they could be causing this code to be set. Do you get any Service Messages on the DIC like Service ABS, or TC or AH?

Bill

 

"why not state what is happening" great idea! Mine is a '97, 41,000 miles. Got a service ride control and service vehicle soon on DIC. Pulled codes, cleared to see what came back, PC P1571 HC, P1644 HC, TC no comm, BCM B0844 HC, RTD 1780 HC. I'm guessing the NO COMM on the TCS is the root problem but guess is the key word. Thanks for all the help.

Richard

 

Having a 97 makes things a little different. From the manuals it looks like it is the only year to have a power relay for the ABS that is controlled by the BCM. Here is some info on it. I highlighted the first thing you should check in bold. It is a relay and relays are trouble prone so I would check it first.

DTC B0844 BCM Temporarily Inhibit ABS

Circuit Description
The BCM monitors information sent between the Powertrain Control Module (PCM) and the ABS system on the serial data line. The BCM can determine if the ABS system can communication this information properly to the PCM. If the ABS system is unable to communicate properly with the BCM or PCM, then the BCM will disable the ABS system by de-energizing the ABSTRANS relay. The BCM supplies power to the ABS system through the ABSTRANS relay by applying a ground to CKT 969 in order to energize the relay. If the BCM detects a malfunction with the ABS system, then the BCM will de-energize the ABSTRANS relay disablabling ABS functions and a DTC will set.

Conditions for Setting the DTC
The BCM is unable to communicate with the PCM and/or ABS system.
The PCM is unable to receive torque level information from the ABS system.
If DTC U1255 is set in the BCM memory as current.
The BCM can only test for this condition when the ignition is in the ON position.
The condition must be present for 5 seconds.
Action Taken When the DTC Sets
Stores a DTC B0844 in the BCM memory.
Disables the ABS system by de-energizing the ABSTRANS relay.
Sends a message to the IPC to display the SERVICE VEHICLE SOON message.
Conditions for Clearing the DTC
This DTC requires an ignition cycle in order to change from current to history.
The BCM no longer detects a communication malfunction with the PCM and/or ABS system.
The PCM receives valid torque level information from the ABS system.
A history DTC will clear after 50 consecutive ignition cycles if the condition for the malfunction is no longer present.
Use the IPC clearing DTCs feature.
Use a scan tool.
Diagnostic Aids
Diagnostic Aids
If the problem is an intermittent loss of communications. Repair this condition first before diagnosing a DTC B0844.
If the DTC B0844 is history, check the ABS system for any one of the following intermittent malfunction:
There is an intermittent open or short (to ground or voltage) in the serial data line.
The BCM loss communications with the PCM or ABS system.
The PCM loss communications with the ABS system.
Damaged or star connector terminals.
Intermittent loss of power or ground to the PCM or ABS system.
Open or shorted ABSTRANS relay.
This is Micro Relay # 37 in the underhood electrical center.
The PCM is unable to receive torque level information from the ABS system.

The P1571 is being caused by the TCS system being shut down by the BCM so you need to find out what is causing the BCM to shut down the TCS.

Same goes for P1644. The PCM is not receiving the voltage from the EBTCM so cannot toggle it to tell the EBTCM how much torque is being delivered.

The C1780 code is a loss of steering data to the RTD system. The RTD gets its steering info from the EBTCM (correct for 97) so if the EBTCM is dead due to being shut off by the BCM this code will show up also.

Your grounds are different than subsequent years also. This is due to the ABS modules being located by the rear axle. The grounds you need to concerned with are G401 and G402. Here is the proper schematic:



The grounds are located at:
G401 Transmission harness, LH rear of vehicle (CKT 150)
G402 Transmission harness, RH rear of vehicle (CKT 1351 and CKT 1251)



Bill

 

Bill, having not seen your post till after I cleaned G103, G104 & cleaned the batt. terminals, I didn't do G401 or G402. However this seems to have fixed the problem. I wonder if the voltage off-on of removing batt. terminals could free a stuck relay? I will check the relay first if this happens again.
Thanks
Richard

 

Cleaning the battery terminals may have solved the problem since a voltage level problem at the PCM could also cause this code to set.

Bill

 

This forum continues to impress! I just got the dreaded TCS no comm and the whole display lit up like a christmas tree. After repeated ignition cycles and clearing of codes, it kept coming back. I just swapped the TCS mini relay #37 with the fog lamp one next to it (same relay) and the problem has gone away (at least for now). If this continues, sounds like a stuck relay.....THANKS CF!

 

And I have not had a (local call) and why???

Im here for you buddy. Just need to touch base! I probably have your answer.


The ZO6 is beyond dead! Give me a call!

Bill in sunny Gales Ferry CT!!!

 

Richard

Believe it or NOT, there have been issues exactly like yours and Bills that are caused by issues INSIDE the rubber accordion tubes between the doors. Dont ask me how it happens but it does. I use to think it was due to a bare wire on one of the connectors but, it was brought to my attention that that bare wire is an audio ground wire. Shake the crap out of the accordion tubes and see if that changes symptoms.

EBTCM ground is located at G-101 (late 98-2004) and at G-104/108 near the battery.



Its at G-402 on (97-early 98)

All I know is,, if you shake both accordion tubes, theres a very good chance that the problem will resolve its self. (been there)