Failed Emissions / No Com
The car has failed emmisions due to no communication at the testing facility. I am able to communicate with three different scanners with all modules in vehicle. This vehicle has a low speed LAN (pin1), Class 2 (pin2), high speed LAN+/- (pin6/14). I plan on to scope each data line and see if the data signals are correct. If I notice anything odd I will start to isolate modules. Also check pin tensions at the DLC. My question is, what data line do emmison test stations connect on? Also is it possible to have a voltage drop/high resistance on a data line that may be affect by emission test station equipment? Thank you and I hope to follow up soon with images of a possible fix
Historically, if it were German, I would suggest that an active fault in the abs would allow communication with a scan tool but disallow communication with an emmisions computer.
The Malibu with 3.5L LX9 doesn't use the Class 2 bus, even though it may be there at the DLC. That is reserved for use on the same vehicle when equipped with L61 (2.2L ) and only then for diagnostics and programming. The HS LAN at terminals 6 and 14 is used for high speed real time data needs. Unlike single wire busses that are not fault tolerant, the dual wire HS GM LAN is fault tolerant…
Thank you for the advice, I was not aware of a parallel leg failure and it still being able to communicate.
Also how did you know that the 3.5 LX9 doesn't use the Class 2 bus? Id imagine this follows the same on many other vehicles.
GM SI. It states that Class 2 is only used on the 2.2L L61 application and not the 3.5L LX9. For the 2.2L it is only used for diagnosis and SPS.
It will communicate on pins 6/14 high speed lan. Have you tried communicating with the pcm in generic mode with a scan tool?In the past I’ve had some modules fail to communicate on the generic side but function properly on the oe side. Almost always there is a reflash available to rectify that concern.
The first scan tool I tried was generic pocket scanner and it communicated fine. Although I have not tried it on my bi-directional scan tools. I am going to be in contact with the dealer today to see if there is a re-flash available.
How many emissions computers have you used just one or more ? If one I will try somewhere else
When I originally had the car last week, I checked for power and grounds at the DLC, communicated with 3 different scan tools. Did a quick check on the data lines to see if there was data being sent. After that I suggested to try a different test lane, considering maybe it was the emission center test equipment. Car failed again on a different test lane.
Emission testing is done via the global side. Can you communicate using your scan tools in generic or just manufacture specific?
Yes I was able to communicate with my pocket scanner. I did not try global with my Bi-Directional scanners.
The EPA equipment is communicating on HS-CAN, pins 6 and 14. Voltage levels are crucial. A scan tool in your shop, whether OE or AM, is more forgiving than the EPA setup. Scoping the network would be a good start.
Have you drag tested the pins?
Didn't have a chance to get to the car until tonight. I first connected my pocket scanner in and it did not communicate. Scoped the CAN +/- through a B.O.B. CAN + was not right as you can see in the attached image. First I drag tested the dlc, it was fine. Dissconted the brake module first then the power steering module, no change in signal and the signal looked good at both connectors. Bcm was
Screen shot from the scanner