QuestionQUESTION: My car keeps fluctuating gears, if I drive at a constant speed it will keep shifting up and down between gears and sometimes sticks in a lower gear, I had a friend look at it a while ago and he said that it was a specific part of the transmission but I'm not sure. So what is the problem?
ANSWER: I'll start by pointing out that there's not enough information here for me to determine whether what you're reporting is normal. I.e., as you apply throttle to go uphill, it may shift down, and when you release throttle to drive downhill or on level ground, it may shift back up.
If we go ahead and presume that you're driving on level ground while this is occurring, three potential causes come to mind:
-- Faulty overdrive switch. If the switch makes intermittent contact, it can cause the transmission to constantly shift between third and fourth gears.
-- Faulty throttle position sensor. This is a major determiner of the gear into which the transmission control module (TCM) will shift the transmission. If the TCM receives an erratic signal, it can cause erratic shifting.
-- Faulty pulse generator. These are the input and and output speed sensors and are the other primary input the TCM uses to determine the proper gear. I'd suspect these to a lesser degree as most often, the TCM recognizes the fault and puts the transmission permanently in 3rd gear (until the engine is turned off and restarted).
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QUESTION: Okay, had my car hooked up to the computer and came up with
P0300- Random/Multipile cylinder misfire detected
P0303 and P0304- 3rd and 4th cylinder misfires
P1624- Cooling fan rely circuit malfunctin (low)
P0734- Fourth gear incorrect ratio
I haven't noticed any misfires or anything wrong with any fans, So are the other problems related, or separate? are they an easy fix?
And what would be the most probable cause for the incorrect gear ratio, would it still be the TCM, or could the throttle position sensor be the problem? Could a transmission fluid flush help?
AnswerThe P0300, P0303, and P0304 indicate misfire issue as you've described. Could be anything causing a misfire. If there weren't any other codes, I might suspect that the transmission is shifting oddly because the car is being driven abnormally due to a severe lack of power from the engine.
But since we have a P0734, I suspect the problem is most likely in the transmission. Basically this code means that the transmission is slipping in fourth gear. I've seen a couple of cases where P073x (slipping gear x) codes were caused by a faulty input our output speed sensor. It cannot be caused by a faulty throttle position sensor, and changing the fluid will have no effect unless the wrong with the fluid is in the transmission. Even in this case, damage has probably already been done to the transmission. P1624 indicates the TCM requested the engine control module (ECM) to turn on the check engine lamp. It has nothing to do with a coolant fan issue.
I'd advise having it diagnosed at the local dealer at this point. Considering the amount of money to likely be spent on repair, it's worth a reasonable investment to have someone run the required tests for a proper diagnosis. I tend to steer people away from chain transmission shops because they seem to concentrate mostly on selling or overhauling transmissions, even in some cases when only a minor repair is necessary.
