Error code only displays when I attempt to read data with a code scanner

I was attempting to read data on my 2009 Chevy Impala 3.5 but I can only see information from the ECM and A/C systems. When the code reader tries to acces the other modules the service traction control light starts flashing and all the gages on the instrument panel turn off. After this event I have trouble code U0073 (communications failure in BUS A). The problem goes away as soon as I stop trying to acces the data. If I just access the ECM then I don’t experience any codes.

There are no service lights on the dash when running normal with no code reader attached.

Sounds like there’s an issue with your code reader. What are you using? Are you looking for a specific problem?

I thought that too but then I tried it on my other car and it works perfectly. My traction control has intermittent problems but no service lights so I wanted look for codes.

What are the symptoms?

Your car has several computers which communicate with each other using a set of wires between all of them termed a “bus” . The “bus” is not just a physical set of wires. It is also a software protocol the computer use to communicate. In other words, if computer A wants to talk to computer b, computer A must issue a specific command of the bus, so computer B knows it is being asked a question, and the other computers also using the same bus know the question is not for them, so they should keep quiet. Something wrong with all that. Or your code reader is not using the correct protocol expected by the other computers on the bus. That culd explain why it doesn’t work on one car, but does on another. The car it works on, its computer isn’t as critical about incorrect bus usage.

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Thank you for the useful insight. I will have to try to find someone with a different scanner to see if the problem persists. I believe the traction control problems stem from the sensors in the wheel hubs.

Explain problem. There are two primary failure modes; the system engages when it shouldn’t or the system is disabled due to a fault.

I have experienced both situations with my GM vehicles and there may be more definitive culprits to investigate based on the clarification of “problem”.

What scanner/code reader do you have?
It is not uncommon for them to support one vehicle/manufacturer but not another. Sometimes it is a matter of a code update on the scanner, others, they are simply not compatible.

When I wanted to see real-time data from my wheel speed sensors, it took some searching to find one that would support my particular make/model and protocol. Once I had it, it was easy to verify one was dropping out at low speeds and causing the traction control to activate… Another time, it was the steering angle sensor failing causing the system to be disabled…

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I’m using Thinkscan Plus S2. It is fully updated and supports my vehicle (or so it says). The only time I have the error is when I try to access my cars data.

The main thing the car does is kick on traction control when the tires are not slipping. There are no stored fault codes for the symptoms which is why I’m trying to access live data.

Under what circumstances; taking off from a stop? Steering straight versus wheel turned make a difference?

I have the same situation right now and it is frustrating and dangerous. Taking off from a stop, the traction control engages and throttle response is severely limited. It’s random so sometimes puts me in a bad situation pulling out into traffic. Project for the weekend- hooking up scanner shortly to see if anything is being flagged and then same as you, watching real time data. I have an Autel scanner which I find not the most intuitive interface. There are many selections to make to get the right operation for my vehicle and if I select something not right from the menu of options, it doesn’t work properly. This seems obvious but the selections are not well documented and how am I supposed to know which ones apply? Trial and error…

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Usually when making turns and accelerating, even just slight turns. Sometimes also when taking off from a stop and going straight. I have found that if I just turn off my trac control it does not do this (seems obvious I guess but makes driving safer). I could just forever drive with the traction control off but there is definitely something wrong.

My bet is on your steering angle sensor being intermittent. I have done two of these now on my Trailblazers. This is the typical failure mode symptoms.

They do not tolerate dithering very well and wear out a spot on the resistance track over time. They seem to be more prone to exhibiting the problem in colder weather which kind of makes sense for what is essentially a big potentiometer.

They are not technically difficult to change but require working cramped into the footwell looking up. If this is your problem, be sure to center the steering and steering wheel before tying the steering wheel to something so it cannot turn. If it turns when you disconnect the shaft, you will loose orientation and likely damage the clock spring. The exchange is fairly straightforward. Good luck!