Symptoms Of Electronic Throttle Control System Troubles
The most common problem I have experienced (and one of the most under-reported) is that the Powertrain Control Module (PCM = Fuel Injection Computer) has a major voltage drop on all of it's Grounds circuits.
In plain English, this means that the PCM does not have a good path to Ground (either because the Ground wires' terminal breaks or gets corroded). The times I have seen this specific problem, I have seen one or all of the following symptoms:
- When you connect your scan tool, the PCM will not interface with it. Meaning you'll get no codes or Live Data. Just a message saying that the scan tool can not link with the PCM.
- A P1518 diagnostic trouble code (DTC).
- Throttle Actuator Control (TAC) Module Serial Data Circuit.
- The Message Board on the instrument cluster will read: Reduced Engine Power.
- The engine starts and immediately stalls.
- This is due to the Passlock sync info, between all of the components that make up the system, being lost.
- You can hear a buzzing sound coming from the engine compartment even after you remove the key from the ignition switch.
- This buzzing usually comes from the Electronic Throttle Body's actuator motor.
- Battery will get drained even with the key removed from the ignition switch.
You might be wondering if just cleaning the battery's Ground cable is enough and I can tell you that it's not enough. Cleaning the battery Ground terminal (at the battery) or where the battery Ground cable bolts to the engine or the chassis is a good idea but the PCM's Ground wires don't connect there.
The PCM's Ground wires unite at a certain point (in the wiring harness) and share the same terminal that's bolted to a point behind the passenger side cylinder head (and this terminal is not easy to access).
Testing the PCM's Ground circuits (all 8 wires) is not hard since all you need to do is to test just one Ground wire for a voltage drop and you're able to test them all (I'll explain how to do this in this article).
Electronic Throttle Body Connector Problems
The second most common problem I've seen, is the Electronic Throttle Body's connector having a copper wire break inside the insulation at the point where the wire enters the connector.
Since the insulation, of the wire itself, doesn't break, you don't realize there's a problem.
The local GM dealerships have always recommended replacing the connector for several years now to their service customers (when an Electronic Throttle Body is replaced by their service department). Well, this is a recommendation that you should follow too.
As of this writing (November 2011), a friend bought one at the local Chevy Dealership Parts Department and paid $180+ (US) for the Electronic Throttle Body Connector (part # PT1572 -GM#88986255), not knowing he could buy the exact same connector online for about a hundred bucks less.
This is where you can buy the components and save some money:
Deposits Blocking The Throttle Plate
The third issue that affects the Electronic Throttle Body is carbon deposit buildup on the throttle plate and on the throttle body bore.
These deposits can jam and/or cause friction that can wear out or break the Throttle Actuator Control motor's plastic drive gears.
Because this is a serious concern, most of the service literature recommends inspecting and cleaning (if needed) the throttle body on a regular basis.
I've written an article on the cleaning procedure and you can find it here: Cleaning The GM Electronic Throttle Body.
