check engine light
May 26, 2010 9:44 AM
Can a used car dealer reprogram the engine computer to suppress error codes from the check engine light?
I am checking out a used car for purchase - 1995 GMC Jimmy SLS, 142K miles.
From what I've read, the 95 and earlier would display the error codes by flashing the check engine light after jumping terminals A and B on the connector. I did that, saw the 1 - 2 code, then nothing. That seems good to me. Is it possible for the dealer to do something to fake this?
I am checking out a used car for purchase - 1995 GMC Jimmy SLS, 142K miles.
From what I've read, the 95 and earlier would display the error codes by flashing the check engine light after jumping terminals A and B on the connector. I did that, saw the 1 - 2 code, then nothing. That seems good to me. Is it possible for the dealer to do something to fake this?
It looks like the 95 Jimmy/Blazer used OBD-II (in fact, it was GM's first vehicle to use it). With an OBD-II scanner anyone can erase error codes and turn off the check engine light. If the error condition that made the light come on in the first place happens again, the error code will be re-set and the light will come back on.
posted by zsazsa at 10:20 AM on May 26, 2010
posted by zsazsa at 10:20 AM on May 26, 2010
zsazsa you rock. That is exactly what I wanted to know. Thanks!
posted by buzzv at 11:10 AM on May 26, 2010
posted by buzzv at 11:10 AM on May 26, 2010
Can a used car dealer reprogram the engine computer to suppress error codes from the check engine light
They can erase the memory, but an unrepaired malfunction will always cause the Check Engine Light to come back on after enough time. The most common used car dealer trick is to just remove the bulb. They're not typically sophisticated enough to hack the ECM in order to change the parameters involved in fault detection. That kind of reprogramming is usually the realm of high performance tuners that need to convince the engine control module to go along with their modifications.
Like zsazsa says, many 1995 cars are OBDII compatible, preempting the 1996 mandated compliance. It might be a little hidden, so check under the passenger side dash or a fuse panel if it's not obvious.
posted by Jon-o at 1:29 PM on May 26, 2010
They can erase the memory, but an unrepaired malfunction will always cause the Check Engine Light to come back on after enough time. The most common used car dealer trick is to just remove the bulb. They're not typically sophisticated enough to hack the ECM in order to change the parameters involved in fault detection. That kind of reprogramming is usually the realm of high performance tuners that need to convince the engine control module to go along with their modifications.
Like zsazsa says, many 1995 cars are OBDII compatible, preempting the 1996 mandated compliance. It might be a little hidden, so check under the passenger side dash or a fuse panel if it's not obvious.
posted by Jon-o at 1:29 PM on May 26, 2010
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Point is, you'll never really know whether someone did go to the trouble of doing that.
posted by tigrrrlily at 10:16 AM on May 26, 2010