Hey guys,

I'm the new owner of a 1999 GMC Jimmy SLT 4 door 4x4 and this is my first post!

I have searched through the forums and have not seen anything like this exact issue, if there is already something posted I apologize.

The problem I am having is with my odometer light flickering. Normally I would just let it go, but it seems like there may be a larger underlying issue. My voltmeter jumps around while going down the road sometimes also, which lead me to believe it was probably the alternator. However, voltage at the battery seems to hold steady at 14v+. Obviously I can't put my multimeter on the battery terminals while going down the road, so I thought I'd plug in the ScanGauge to make sure my dash voltmeter was right.

This is where it gets strange- upon plugging in the ScanGauge, the issue is gone. No flicker in the odometer, and the voltmeter in the dash reads the same as the ScanGauge- right around 14v steady, regardless of how much I turn on (headlights, blower motor, radio, etc.)

Here are some other strange things I've found:
-The flickering only happens with the headlights and the radio lights on. If I turn the headlights off and/or turn down the dial for the interior lights (to off) then the odometer is bright and doesn't flicker. This made me think possibly the issue is in the switch, but why then would the ScanGauge make it stop??
-Also, if I unplug the "ILLUM" fuse, which lights the radio and dash, but not the odometer, then my service engine soon light comes on... That one really gets me. I think the light probably should always be on (I just bought the vehicle and it's likely overdue for an oil change), but it only comes on with that fuse pulled from what I can tell.

Another side note (probably unrelated, but trying to be thorough) is that when I take the key out of the ignition when in park the interior lights don't come on and the radio goes out immediately.

The battery has a "6/2013" sticker on it, and the alternator is not original either from what I can tell. The Jimmy is from North Carolina, so luckily it doesn't have the typical Michigan rust that I usually see.

If anyone has any ideas I would surely appreciate hearing them! I'm a college student and don't have a lot of money to through into guess-and-check part replacement.

I am, however, more than willing to put in the time and effort to learn and do any diagnostics that I am capable of. Thank you!

-Mike

 

starter going bad or loose connections to starter.

 

Thanks for the reply jkyle187!

Today while driving my service engine soon light came on and the code was P0327, "Knock Sensor Circuit Low Input".

Could this be the cause of my problems instead of the starter, or do you think that they are unrelated?

Thanks again, I appreciate the help.

 

Erratic system voltage could be caused by inaccurate control over the alternator output by the PCM. One thing you can try is to convert the alternator from PWM control to reference voltage control. I believe there is a tech article on this task. See where that gets you concerning your voltage issue.

Looking at the schematic for the ILLUM fuse, there should not be anything on that circuit that would cause the CEL to illuminate. the only thing I can think there is that someone has tapped into that circuit to supply power to something else for some reason.

Concerning the P0327 code, have you checked out the code listing section?
P0327 (S-series) - Knock Sensor 1 Circuit Low Input

The knock sensor (KS) on your truck is a single wire sensor that gets its ground through the main engine ground. The KS is located behind the driver side cylinder head and can be a pain to get to. If a continuity test of the wiring from the PCM to the KS shows that the circuit is intact, I would test for proper engine grounding to battery negative. If there is a problem with ground distribution, it can cause all kinds of weird things to happen.

 

Thanks for all the info swartlkk! I'm hoping to get it into a garage this Wednesday to start troubleshooting and testing some of the things you pointed out. If I find out any other helpful information I'll update it on the thread.