Instrument cluster on the fritz, truck randomly downshifts...

[Chris_North]

A few weeks ago just down the road from my dad's house my truck out of nowhere shut off and the dash lit up like a christmas tree with the gauges reading way out of range of what my aftermarket gauges were reading. I started it back up, but it was running extremely rough, almost as if multiple cylinders were missing. I pulled into a nearby parking lot, checked some of the obvious things, but couldn't find anything wrong. When I slammed the hood to make my way back to the house the problem cleared up. I couldn't find anything and it ran better than normal until a few days ago when the gauges and indicator lights were lighting up randomly again. I had no choice but to drive it as it was, then the problem cleared up again until today during my commute to work. I wouldn't make such a big deal of it but now every once and a while the trans will randomly downshift for no reason on the highway for a few seconds then shift up again. Then around town after making a turn it seemed to shift up, then want to shift up again, then shift back down ( or something like that; it happened in the span of two seconds so it was hard to tell exactly what was going on).

As far as the cluster goes at least one but frequently all of the following are happening: OP reading too high, coolant reading too high, voltmeter reading too low, gas gauge reading too low, air bag light flickers or lights dimly and gets brighter on acceleration, ABS light comes on, and the "check gage" light comes on (I think this is to do with the other gauges reading out of range of acceptable more than anything else).

I pulled apart the main ECU plug and checked and cleaned it but there was nothing to note. I also pulled apart the molex plug that sits on top of the intake and cleaned as best I could because there were a few pins that had a white film of corrosion on them. I pulled out the instrument cluster and checked all the plugs connected to that and they all look good, and I randomly checked a bunch of plugs in the dash while I had everything apart and they all looked good as well. Pulled a bunch of fuses and relays: nothing unusual. Not sure where to look next.

I have to admit I don't understand exactly the purposes of all the modules and control units scattered around under the dash and listed in the manual. PCM, GEM, and I forget the other one. I also have no idea how the cluster works; if the gauges get their signal directly from the senders or if they all go through a controller first. I am nearly certain I have adequate voltage despite what the cluster indicates as I have an audio system with a large cap with a built in voltmeter that reads between 13.8V and 14.3V depending on how many accessories are on. Same thing with the oil pressure. What really gets me is that I'm fairly certain the OP sender is a simple open/close type (I know stock ones are, this one was changed trying for something else) so I don't get why it would read higher when most of the other gauges read lower. Additionally, the airbag light will illuminate when first turning the key (like the lamp test), indicating to me that the AB module is functioning, but after it goes out it comes back on very faintly and will get brighter as the engine revs. Occasionally a large bump will set everything back to normal for a little bit, but another bump will throw it back or it may just start happening again on its own.


Anyone got any ideas?

Forgot some vital information:

The vehicle in question is a 98 Ranger XLT with the 3.0 and auto trans. It has a butt-ton of electrical accessories added, most recently a Flex-a-Lite for the rad and a trans cooler with integrated e-fan. Everything gets power directly from the battery, including grounds. There are only a few relays for control hooked into the interior fuse panel for key-on power via fuse taps.

 

[97RangerXLT]

Loose ground? Possibly faulty ignition switch. ..slamming the hood made the them work again.

Sent from my SCH-I535 using Tapatalk

 

[adsm08]

You have a loose connection, and probably too much load if you have "a butt-ton" of electrical stuff added on.

 

[Chris_North]

You have a loose connection, and probably too much load if you have "a butt-ton" of electrical stuff added on.

Yeah I kinda figured haha. I just have no idea where. If it comes to it I'll pull every plug apart and check it, but that's a lot of plugs and TBH I don't even know where every single one is. The one that's the problem (if all it is is truly a loose connector) might be overlooked because it's behind something and I didn't think to look. I'm good at shotgun troubleshooting, but to do that seems more like carpet-bombing. I have already pulled several plugs apart and attempted to jostle several more. No change.

The thing is the majority of all accessories are low load and intermittently operated. Auxiliary lighting and cheap-o mini air compressor and the like. The bigger stuff like the plow pump and winch haven't seen use in over 6 months. Not that it rules it out but like I said volts never drop below 13.8V, even with headlights, heat blowing, and stereo comfortably outputting.

I had considered loose ground but at least from my understanding the cluster gauges operate off of being grounded from the senders in the block. The OP sensor at least should read zero I would think if it was a grounding issue. If it was a ground to a controller of some sort then I would agree, but if and which controller are what I need to find out.

I'll pull apart more stuff tomorrow afternoon and see what I can find. There's some part of me that thinks it's a bad computer someplace, possibly a loose connection on one of the boards, but I don't know.

I'm correct in assuming the instrument cluster is nothing more than a set of lamps and gauges with the diodes and resistors necessary to function and that it has no direct control over anything right? Is it possible the ECU is malfunctioning causing the dash issues and trans shift problems? The ECU is what controls the electronic parts of the transmission correct?


Edit: Dome/map lights have apparently also ceased to function at some point. They were definitely working a few days ago, before I started having any trouble. I wouldn't have noticed since then before tonight. This could be a coincidence or something stupid like a fuse but it's too late and dark to check. Seems awfully strange though.

 

[Chris_North]

Alright more developments. Truck shifts completely effed up now. Won't shift out of first until 4000RPM then it shifts rough. All kinds of weird up and down shifting for no apparent reason. OD light was flashing and I couldn't shift into first gear at all, even with the shifter manually.

OP gauge flickers. Speedometer stopped working. All the other original problems. Very faint hot/burning electrical smell if you put your nose near the steering wheel, but I can't pinpoint it further than that (hell could just be something on the wheel). I pulled apart a bunch of connectors under the hood and found some with minor corrosion, but nothing too bad. Cleaned and greased them all, no change.

Would anyone be able to check to see what voltage they get to the oil pressure sender? I got 8.6. I know it's got to be something stupid, a bad connection or a malfunctioning module, but the wiring diagrams I'm finding are confusing. Everything seems to be connected unspecifically to something else. There's 50,000 plugs connecting 80 components controlled by what seems to be 200 modules. If I had a starting place I would be much better off.

 

[Andy D]

Check for good battery connections and the ground straps between the frame and the engine and the engine to fire wall.

 

[Chris_North]

Alright here's where I'm at. I pulled apart, cleaned and greased a bunch more connectors and inspected the harness. Nothing remarkable found.

I spent a bunch more time on alldata looking up schematics, ground connections, and connections. The site has a lot of information to offer, but it takes a research team to find it. Everything I'm having problems with, the speedometer, the indicator lights, the dome lights, the chime, and now the windshield wipers, is apparently all controlled by the Generic Electronic Module. I was nearly 100% convinced this was the problem and have been waiting for a replacement to arrive for over a week when today I played around with my truck a bit more. I unplugged everything from the GEM, but it made absolutely no difference. I still have exactly the same issues with absolutely no perceivable change. Ordinarily I would think this supports my theory of a faulty GEM, but I'm having the same issue with the gauges being on sorta funky and the airbag light glowing faintly and getting brighter with an increase in RPMs.

Am I correct in believing the GEM is the only thing that controls the instrument cluster? If not, what does? I also tried unplugging everything from the gauge set and it changed the way the engine sounded? What the hell is going on?


Either way a used GEM is on its way, but it is a used part, and from what I've read it is possible it will not work correctly until it is programmed at a dealership to match the options of my specific truck. I'm worried that the replacement GEM is not going to help, and worse, that it no helping doesn't disprove that it's the issue because there are more hoops to jump through than just plugging it in.

So can anyone enlighten me at all?

 

[Andy D]

No experience with Rangers, but my cars need pos and neg battery and the signal ground to make the gauges work.

 

[Chris_North]

It would seem from the way the wiring diagrams that this is the case with the ranger too. I'm not sure how it's supposed to work.

I got the replacement GEM today. It's numbering is slightly different: instead of ending in an "E" it ends in a "D". I plugged it in and went to start the truck and the battery was dead. Jumped it and the engine cranks but will not start. No lights. No wipers. Either from plugging in a new box or just sitting for a few days, I am now even worse off than before. It won't start with the old GEM, the new GEM, or no GEM, which is quite hilarious considering I was able to start and run it fine just last Friday.

The only ground I have not verified is the one that's supposed to be behind the kick panel someplace. I'm pulling and verifying every goddamn fuse with the ohmmeter, then I'm going to start going across pins on the plugs and checking for power and continuity to ground. After that I'm pulling my stereo, speaker, and tools out and setting the effer on fire and laugh as it burns.

 

[txgocartB3000]

Where you located at?

I have a free day this weekend maybe you are nearby.

Ray

 

[Chris_North]

I'm assuming you're offering to help and not watch me light anything on fire haha. If so thank you that is very kind, but I am located in eastern PA, so that's a little out of your way...

 

[txgocartB3000]

A little far for a day trip.

Don't get discouraged, step back and regroup.

It's been 25 years since I stopped drinking but a cold glass of tea sometimes helps.

Ray

 

[Chris_North]

Well only if you don't own your own plane...

Thanks. I know I'll get it eventually. I just need a few nights of good rest to clear my head. I still drink on occasion, but that's not going to help me figure anything out. I'm sure it's something you can agree that being drunk to me seems like such a waste of time.

 

[Chris_North]

Made some progress yesterday.

After charging the battery the truck fired right up no problem. Best guess is that despite being strong enough to crank the engine, the battery didn't have enough power left to supply the necessary voltage to the engine circuits. Battery voltage dropped down to 5V while cranking. Hopefully that was the only reason for that, and if so, that's one down.

Checked every one of the fuses. Nothing blown, BUT I find that one of the GEM fuses was missing. My guess is that I unplugged a fuse tap plugged into that spot while troubleshooting the original issue and didn't notice it. It was toward the back and blocked by one of the unplugged taps. Interior lights, wipers, chime, speedometer, and other GEM related functions are back and seem normal. I took the truck for a very short test drive (but did take it up to 50MPH) and it seems to be shifting and running great.

So while it would seem that many issues were a direct result of trying to fix the original issue, I'm still having a lot of other electronic issues that are the result of whatever the original problem is. Air bag light is still coming on and getting brighter with increased engine speed and the oil, battery, coolant, and fuel gauges are not accurate. I dug into the gauge cluster a bit and found one diode that controls the operation of the coolant gauge bad, but with it removed from the circuit I lose function of the gauge but nothing else improves.

I'm having a difficult time understanding the operation of the gauges. They both get a positive and ground signal, in addition another positive and then another ground through whatever sender controls them? I have tried unplugging the connector that sends the signal for the airbag light to the cluster which does cause the light to go out, but the other gauges (which according to the diagrams I have do not get anything from that plug) still function abnormally. Additionally, when I unplug that connector the dome light gets dimmer and the gauges flicker slightly. Plugging it back in and the light gets brighter and I can hear the alternator straining. I am certain there is something shorting and/or backfeeding someplace, but I don't know where. I have tried unplugging the airbag module (which I never believed to be a problem) and no real change. The light comes on solid (to illuminate an issue with the module, ie it's not there) but nothing else changes and I can still see some flickering with the AB lamp.

At this point I'm assuming the GEM itself is okay, but I know for sure I had issues with downshifting at the same time the lights and gauges started malfunctioning. I think the downshifting is likely the result of shorts and weird signals screwing with the GEM's processing. Today I was planning on taking readings from the pins of the gauge cluster plugs and try to determine whether the issue is in the cluster itself (I do not believe it is) or somewhere in another module or wiring. It's difficult without a benchmark to compare to, and trying to match up where specific circuits go on the wiring diagrams is proving to be difficult.


I was planning on working more on screwing with it today, but instead I stayed in my pajamas, watched TV, and ate pancakes. This is my first lazy day in nearly 6 months, so I'm enjoying it as best I can.

 

[kbecker3]

When you figure it out please post your findings, as i will be very interested in this. My 02 ranger did this once like 3 years ago... Gauges went nuts, truck started shaking like missing, warning lights were going nuts.... after i got out and didn't see anything weird under hood, slammed hood shut, problem went away and has not re-surfaced since... But if it does, i should would like to know where to look...