i have a 95 z and my check guages light is on. the thing is, the light is only half way illuminated. when you start the car, the light fully illuminates like it should. a few seconds later it is suppossed to go off but it goes to being half illuminated. i am not sure what to check. all of my guages in the car look good. i was told that it could possibly be my alternator with a problem inside of it. however, i had it checked and the diodes were ok and the charging was good. any suggestions?

 

That bulb is powered by switching ground. The positive voltage goes directly to the bulb. The PCM will connect the other side of the bulb to ground when it wants to illuminate it. The symptom you talk about could be caused by 2 things but one is more likely. The ground side of the bulb (wire from PCM to bulb) could be contacting ground slightly. This is highly unlikely since the problem is the same and has not gotten worse and is not intermittent like bare wires usually are.

The more likely cause is the output device (driver) usually a transistor is breaking down leaking to ground. When the PCM turns on the lamp, it drives the transistor fully open but when it's not being driven, it's leaking.

Don't know much about the internals of the PCM. It probably does not have individual xsistors. More likely they are ganged together in an IC. Therefore it may be more combersome to change the driver. You may have to find a used PCM to fix the problem.

One way to check is to disconnect the connector at the PCM (sorry haven't found which one is the lamp circuit) If the lamp goes out, the driver in the PCM is the bad guy. If it stays on, there is a bad spot in the wire.


Good luck

 

thanks for the help. you kind of lost me because i don't know much about pcm's either. is there any way for me to find out which connector i should try to disconnect?

 

I stand (or sit at the computer) corrected. I have racked my brain all day over this one. What I told you before about the driving device of the bulb "leaking" is correct and the ground is switched to turn the bulb on or off. BUT I found the check gauges bulb is turned on by a solid state module located in the instrument cluster. I was incorrect in thinking the negative side switching came from the PCM. This module located in the instrument cluster will take input from coolant temp. oil pressure and oil level and signal lights to come on, independant of the PCM. The PCM gets it's signals as well but this light and 2 others are signaled by this moldule.

This module is why your light is on dimly all the time. The big question is "is it replaceable" or do you have to get the whole instrument cluster. Perhaps someone with a parts lookup can tell you. You could check a junk yard and look at an instrument cluster.

Sorry I took so long to get back to you.

 

first off, thats no problem that it took some time. you were a great help. i had no clue where to start. so overall your saying i just need a new instrument cluster? by the way, i do have a low coolant light that is on but the coolant is not low. i just figured it was the sensor and i have not got around to replacing it yet. i wouldn't think that sensor would have anything to do with it since the check guages light is only half way illuminated. your help is greatly appreciated!!!!

 

Well hopefully you can get the module without buying the whole gauge cluster. I just looked at the low coolant indicator and see a couple of things. One is the coolant level sensor which turns the light on. The other is a coolant level latching module. I didn't see much about these other than a trouble shooting guide that says either the sensor is bad, the signal wire is shorted, the Retained Power Module is bad (that's what keeps your radio working when you turn the car off) or the Low coolant level latching module is defective. I still haven't found them yet. I'm still looking for them. I'll let you know when I find them. Rob may be able to tell you where they are.

See ya

 

thanks, i really appreciate your assistance. i don't know about all of these modules, but the coolant sensor is known to go bad or gum up and its just on the side of the radiator. if you find anything out, feel free to let me know. thanks