2001 Suburban Intermittent Shift Problem

Two thoughts come to mind with your transmission’s symptoms.

• A sticking solenoid
• An intermittent in one of the sensor clusters

In both cases, honestly, there’s something shorting somewhere that is causing the problem.

The first place I would check is the solenoid cluster on and in the valve body. The good thing is that at least one of the solenoids is on the outside of the valve body so it is easily accessible. The not-so-good thing is that your technician will have to do a partial transmission teardown to access the innards of the valve body. If it seems like a bit of overkill to have the solenoids split like that, I agree. However, it is understandable in light of the fact that the solenoids were likely added one-at-a-time over time. This has given them the odd placements.

Placements aside, it does sound like one of the solenoids is sticking. To test it, your technician should put a small current into the positive side of the solenoid. Every time he applies the current, the solenoid should click on. If it does not, say, after 10 good tries, you have found the culprit.

Replacing a solenoid is the least expensive major service. It is a major service because it requires a partial teardown of the transmission It should cost about $150 for parts, although the labor is somewhat big if your tech has to go inside the valve body. Overall, labor should be about $550.

The other possibility is a short in one of the sensor clusters. By the sound of it, it could be — and most likely is — the throttle positioning sensor. The throttle positioning sensor tells the transmission control unit whether your vehicle is accelerating or decelerating from the force you apply to it.

If the throttle positioning sensor is shorting, telling the transmission control unit a bit of misinformation, it is very likely that you will experience the performance you are describing.

Let’s say that the throttle positioning sensor is okay, where else could the problem be? More than likely it is somewhere in the electronic cluster that control the transmission. Since the tranny may have eight or more sensors working, at any given time, and since some of them may even be within the engine bay, rather than the transmission, it will take time to track things down. However, if your technician has patience, he will find the answer, now that he has, at least, a suggested direction for hhis investigation.