We have had some intermittent ABS and TCS dash.

  • 70,000 MILES
We have had some intermittent ABS and TCS dash lights on for the last 6 months.
Recently however, during the first km or so of driving out of the residential streets we live in, the ABS system has been modulating / pulsating along with the brake pedal. Once we get the car up to speed the problem goes away and does not return until the return trip home. The ABS and TCS lights again are off and on when this is happening.
I pulled the 2 ABS fuses (why are there 2?) And the problem does not happen, but now the ABS, TCS, Brake, and Engine lights are on.
Any Advice and Help would be great
Do you
have the same problem?
Monday, January 7th, 2013 AT 8:33 PM

1 Reply

You're describing false activation, and the computer is detecting a problem and telling you about it. The most common causes for an intermittent problem to be detected while you are not applying the brake pedal is a cracked tone ring at one of the wheels, or a mechanical problem with one of the wheel speed sensors. In general, a mechanical problem causes no speed signal to be generated and will be detected after the car starts moving. An electrical problem such as a broken wire can be detected any time including when the engine is first started but before the car starts moving. Once the light has turned on there will be a diagnostic fault code stored in the computer. The place to start is by having those codes read. They never say to replace parts. They only indicate the circuit or system that needs further diagnosis.

The Traction Control system is an add-on to the ABS system and uses some of it's functions. It's common for that light to turn on also because the computer knows due to the ABS problem it can't run the traction control system properly.

There will always be two fuses for anti-lock brake and air bag systems. If there was only one feed circuit, there would be no power to turn on the warning light if that fuse blew.

One other important detail to be aware of, especially common for GM owners, is there is always a long list of conditions that must be met before a code will set. One of those conditions is there can't be certain other fault codes already set. The computer compares many things to figure out when there's a problem. For example, when driving straight ahead, all four wheel speed sensors had better be reporting the same speed. If one sensor has a problem and a fault code is set, the computer can't use that as a reference so it may not set another code if a different speed sensor develops a problem. That second code will not show up until after the first problem is fixed. That is the source of a lot of frustration among GM owners and mechanics. That problem rarely happens when a new problem is fixed right away. When it is ignored for a long time, as you've been doing, there is a lot of time for a second problem to develop, and there may be no fault code set for it yet. Even when your warning light turns off, any codes remain in memory and can prevent additional codes from setting. What this means is once the original problem is identified, diagnosed, and fixed, it is possible for the warning light to turn on again with a new code in memory.
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Tuesday, January 8th, 2013 AT 2:39 AM

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