I just repaired a 2010 Equinox with a complaint of ABS light on and Service Stabilitrack message displayed. The vehicle started and ran normally driving into the shop and the light and the message were displayed as in the complaint. My first test was to check for codes set. I did a vehicle code check of all modules and saw only these codes set in the EBCM.

[2010 Chevrolet Equinox LT, ECM/Inputs/Outputs Scan Data]

The problem seems to be limited to the HS Chassis Expansion Bus, although the EBCM is also on the main HS bus. That calls for a fast look at the main HS bus first.

[2010 Chevrolet Equinox LT, ECM/Inputs/Outputs Scan Data]

The voltages are normal. Let's see if the EBCM is present on this bus...

[2010 Chevrolet Equinox LT, ECM/Inputs/Outputs Scan Data]

OK, it's present on the HS bus, how about the expansion bus?

[2010 Chevrolet Equinox LT, ECM/Inputs/Outputs Scan Data]

Well, no modules are detected and the bus is shown as CAN Bus open. Let's see if it is...

[2010 Chevrolet Equinox LT, ECM/Inputs/Outputs Scan Data]

It sure looks like it is either open or shorted to ground. With key off, I checked the expansion bus resistance and saw 61.2 ohms and normal resistance to ground on CAN A and B. So, it's neither open or shorted to ground with key off but low voltage with key on. Why? There are other possibilities. With key on, engine off, I cleared codes and noted that the codes did not reset immediately. Monitoring the codes set, this was the first...

[2010 Chevrolet Equinox LT, ECM/Inputs/Outputs Scan Data]

After 20 seconds more, this was set...

[2010 Chevrolet Equinox LT, ECM/Inputs/Outputs Scan Data]

And 30 seconds later...

[2010 Chevrolet Equinox LT, ECM/Inputs/Outputs Scan Data]

Time to analyze data collected. The first code set was by the PSCM for invalid data from the SAS. Since the PSCM is not on the expansion bus, this data must be transferred between buses by the EBCM. Next codes set were from the EBCM showing Can Bus B off and a loss of communication with the MAASM. And the third code set was from the EBCM losing communication with the SAS. What does all this mean?

The first problem detected was invalid data from the SAS. If the EBCM sees invalid data from either the SAS or the MAASM, it can shut down the CAN Bus and substitute values for these modules. Once the Bus is open, the other two modules cannot communicate with the EBCM and codes were set for loss of communication. What's the best way to prove this theory as we cannot read any data on this bus to help us. I unplugged the SAS and jumpered the 4 com lines and rechecked the expansion bus voltages, seeing this...

[2010 Chevrolet Equinox LT, ECM/Inputs/Outputs Scan Data]

OK, we now have an active expansion bus again. I installed a new SAS and rechecked the bus for modules present.

[2010 Chevrolet Equinox LT, ECM/Inputs/Outputs Scan Data]

Everybody is present and talking together now and the lights and messages are gone. A little thought analyzing the failure can go a long way.

James from Florida

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