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Chevy S10 - GMC S15 and Sonoma Electrical Problems



  • 1998 GMC Sonoma, runs fine for a while (30 minutes or so). Then the volt gage begins to "twitch", it drops below 14 amps, and pulsates with the turn signals. After 30 seconds or so, it then drops to 12 amps maybe 11 amps, and the truck then dies. When driving, it is not unusual to watch the volt gauge begin to pulsate and drop till the truck dies. Wait a few minutes...can drive again..till next episode. Replaced the battery, alternator, fuel pump. Question is, is there something that regulates the electrical system? I've had the alternator checked out, and the shop says it is functioning normal. Accellerate, air conditioning on, the volts guage drops on their equipment. Run the AC in the real world driving, and I don't have a prayer in getting to where I'm going. It will die. Any ideas? suggestions?
  • gonogogonogo Posts: 879
    This how I check out an electrical system. I put a volt meter across the battery terminals to read voltage. I then load the system and watch my voltage readings. At 1500 RPM the voltage should be at least 13-13.5 volts with everything on.
  • hoodlatchhoodlatch Mid-westPosts: 255
    Sounds like you might have a corroded cable or wire. After it gets warm from the current, it stops conducting all together. Sometimes bad cables are not obvious to the eye because the bad spots are hidden by the plastic insulation. Or sometimes you might have a bad ground connection. In both cases they start out part time vice full blown problems, which makes it hard to trouble shoot.

    I don’t understand why you changed the fuel pump though. That’s a monumental task in itself.

    When I have radical electrical inconsistencies I usually start with the battery cables and go hand over hand, step by step looking for flaws. Things like where road salt and slop have been working on connections. Also, if I come on a cable or wire that has a lump in it like a snake that just swallowed an egg, I would consider it suspect.

    As you can testify, most automotive electrical problems are time consuming. Let us know what you find out. Good Luck :)
  • Replaced the fuel pump because I found out it was in the gas tank. Truck only died when the weather got warm and someone suggested that fuel pumps were faulty (original) and would shut down when they got warm. After replacing it, I was told it was faulty - although now I'm still not sure if it was or wasn't. I've had this problem for going on 4 years now.

    So it could be almost any electrical cable then??
  • hoodlatchhoodlatch Mid-westPosts: 255
    Four years! Your patience is that of a Saint. I think in my case, I would be looking for a Thermite grenade.

    To answer your original question on what regulates the electrical system – on GM’s for many years now the voltage regulator is built into the alternator. Since you have changed out the alternator and still have the same problem, it is unlikely the regulator was the culprit.

    I wouldn’t say the electrical problem is just any cable or wire. But I would suggest the break down or slow down in the electrical continuity has to do with a leading or predominate cable or wire. Maybe loose connection, loose bolt to a bonding strap, bad terminal eyes going to alternator, loose wiring harness junction going through the firewall, wiring cable going into battery cable lugs corroded to the point only a couple of strands are left, these all are points of interest.

    Put on your gloves and your Tom Terrific thinking cap. You don’t have to worry about breaking it if it’s already broke. Part of being an effective “Shade Tree Mechanic” is tenacity. Good luck Champ. :shades:
  • Chevy and Gmc do not know how to make a dependable truck get a Ford Ranger or a dodge dakota. I am yet to have any trouble with my Ford or my dodge both of them have over 200k miles
  • hi, i have a 1992 sonoma and all the sudden my tail lights and turn signals stoped working. my head lights still work but none of the other lights do. on my dash the two turn signal lights are lit up when i turn the lights on and when i push the brake in the two turn signal lights come on until i let of the brake pedal. i have no idea what happend to it of how to fix it????
  • bcherrybcherry Posts: 1
    I have a 1997 GMC Sonoma and just today the blinkers stoped working. I checked the fuses and are all fine and some how the hazzard lights work. The blinker switch gos on when I put the bilnker on but the light does not and after a turn It shuts off. If any one can help I will be very thankful.
  • hoodlatchhoodlatch Mid-westPosts: 255
    Sounds like either the flasher for the turn signals are kaput (unlikely) or one of the bulbs is defective. The emergency lights have their own flasher. Sometimes water gets into the parking and taillights that causes them to corrode. Being that your emergency flashers work, turn them on and walk around checking for defective lights. Chances are that what ever the problem is its related to a bad ground, bad bulb receptacle, or burnt out bulb. Good luck. :)
  • blazer74blazer74 Posts: 1
  • mh60gurumh60guru Posts: 3
    I signed up for this website because of your post. I have a 98 S-10 2.2L with the identical problem. I've replaced the alternator, which seemed to work for a month or two because my volt meter held steady at 14 amps. But the problem is back with my meter usually reading about 13. Then occasionally it will begin to drop and even twitch when a turn signal is on, just like yours. Once it gets down to about 10-11 my electrical goes hay-wire and the truck dies out. My truck is a manual so I can put it in neutral, and restart it as I'm coasting down the road...and it will run fine. This may happen a few times in a day and then no problems for weeks!

    Everybody I've talked to has of course told me that there's a short or loose ground somewhere. I've cleaned every connection and ground that I can get to. The only thing I haven't been able to really check is the starter because you have to remove the exhaust pipe to get to it on the 2.2L and those bolts are not coming off for me in my driveway. Have you had any luck figuring out your problem? Thanks.
  • gonogogonogo Posts: 879
    I have a 99 2.2 Sonoma and I can drop the starter with out removing the down pipe.
    Can't remember the exact procedure but it was easy. I think both support braces and the cross bracket.
  • larry71larry71 Posts: 1
    Yesterday while backing out of driveway my AC/Fans quite working. In addition the radio/clock stopped. Clock/radio came back. Then fuel gauge/temp gauge went out. Back on this morning. yesterday the wipers/wash would not work. Still don't. Lights for what gear you are in are out. Come on briefly on start. Wipers/wash out. If radio is on and I swith on AC to see if it works radio goes out. What is going on?
  • My 98 S-10 (2.2L w/135K miles) also has a wandering dash voltmeter. I have cleaned, inspected, and replaced every ground connection, both visible and hidden. New battery, starter, and alternator haven't made any difference. The problem is unpredictable, has once put the battery light on, and even caused stalling under load. I have just purchased a $600 scanning tool and discovered that no codes are stored. The voltage data taken, while parked and driven, is what the ECM sees. The dash voltmeter is showing the actual reading, going into the computer, regardless of the battery terminal voltage. I am reading, at the ECM, 13.5V to 14.2V under normal conditions, then the slow decline begins and can drop to 11.9V. Then , without warning, go back up to the 13V+ range. My next step is to install a new ignition switch which I've just received. It is a scary looking 22 inch mass of 13 wires and four connectors. I'm still looking for a decent reference for installing it. Also, I just ordered, from the dealer, a full set of pos. and neg. battery cables for $216, including the 175 amp fuse for the cable junction block under the battery tray. Oh, and I have a good SW ammeter going into the circuit to compare to the voltage readings. I will report on the results after all the new stuff is installed. I'm convinced that this is an age/resistance/temperature problem that is affecting the charging system. Voltage doesn't just change unless current and/or resistance changes, too (Ohm's Law). I think we're all chasing symptoms, when the problem is an inadequate primary system that overwhelms the alternator and battery. I'm thinking a FOR SALE sign might be added to my list.
  • gonogogonogo Posts: 879
    Your on the right track with the ignition switch, common problem on high time trucks. $216 for battery cables, oh my gosh, I would have bought aftermarket.
  • wearthywearthy Posts: 2
    I have the same problem I have 3 diffrent dashed and none of them work they could all be junk but i dont know have you salved your problem yet?
  • wearthywearthy Posts: 2
    It is the chip on your key go get a new key made
  • Thanks for the info Oldtimer7. My next step is also to replace all of my battery cables. But I'd like to wait until you post your results since they are $216 per set! And just as an update, my truck died on me three times on the way home from work to day. It's an ill feeling just watching the volt meter drop and knowing that it's going to die in a matter of seconds. If I don't figure something out soon, I may just skip the FOR SALE sign and go directly to pushing it off the nearest cliff! If so many people have had this problem, why hasn't Chevrolet addressed this!
  • This is a quick update while I'm waiting for one more cable to arrive at the dealer. These cables don't look like anything you've handled before. Complicated! The ground has three connections (chassis, body, and engine); the positive from the battery goes to the starter (one cable), to the junction block under the battery tray with a 175 amp fuse (second cable), from the second post on the junction block to the alternator with a fuse link (third cable), and a separate fourth cable from the first post on the junction block to the other side of the engine compartment where the first of two fuse panels exists on the fender apron. Aftermarket won't go near these!
    I had a long talk with the regional electrical guru from GM who visits all the local dealers to solve whatever the regular techs have given up on. Here are some highlights of our discussion . . . .
    1. There is NO single item that shows up in these complaints that prompts the techs to head for a common culprit.
    2. My developing conclusion that it is a charging problem is correct. The voltage regulator is confused!
    3. The entire primary system is too long, has too many connections, and deteriorates in various parts of cables and connection to contribute to an increasing resistance that taxes the limits of the alternator.
    4. The fluctuations in the dash voltmeter are exactly what the computer is "seeing".
    5. Measuring the voltage at the battery doesn't tell you enough.
    6. The battery must be checked for specific gravity by cell, and load tested to verify if it is healthy enough to be eliminated, or is a suffering contributor to the overall problem. Remember, it becomes a victim of poor charging.
    7. The fluctuations in the voltmeter are showing the actual response of the voltage regulator to the system demands.
    8. The alternator is not strong enough for the applications.
    9. The regulator (inside the alternator) is controlled by the PCM which is not always calling for the correct response from the alternator. Because the system combines so many loops, the power budget is often confused as to the correct voltage/amperage.
    10. ANY deterioration in the system of circuits (large or small) contribute to misleading readings within the system monitored by the computer.
    11. The battery cables, all grounds, and connections must be in primo condition. Since current is flowing in so many directions, any marginal conductivity is curtains.
    12. Be careful to avoid questionable aftermarket components since the items may not be close enough to OE specs to really repair the problem.
    13. Sometimes the dealer has the only quality Delphi part that you want to invest in.
    14. This whole issue is a prime example of what we have to look forward to when ever increasingly complex vehicle systems get old. This is the classic example of the engineers not being there to see what they've created many years down the road. Remember, we do the real testing, and this one is failing. For us to eliminate all of these electrical headaches, we have to keep the systems and circuits as close to "new" as possible.
    When I receive the rest of my stuff from the dealer, install it, and test it, I'm going to make my results known. I do still intend to change the ignition switch which might require pulling the steering wheel (air bag!). Still referencing this one (?).
    I used to be a repeat Ford truck owner, right now I doubt the I'm going to dwell in the GM camp much longer. I'm tired of consoling my friends who drive Dodges . . . . . what do I turn to (Japanese?)?
    If you have any questions, please ask me.
  • gonogogonogo Posts: 879
    Oldtimer remember when the bat cable positive went to the starter and all other positive feeds went from there.
    I would not pay for $216 battery cables.
    I have lived long enough to know there is a work around to most any thing.
  • i have also had the same trouble i bought a piece of 4GA high voltage cable and rerouted the starter wire because i found mine wedged into the motor mount and was just about cut in half
  • crealcreal Posts: 1
    I've put new wires ,coil, dist., coil control unit all of these I've put on twice since december tried high performance ignition parts too. Still night inspection looks like a lazer light show..
  • gonogogonogo Posts: 879
    Try OEM wires and plugs.
  • I have a 98 S10 and it blows the AC fuse every time the switch is turned to any AC mode but if I replace th fuse while turned to Vent and the blower and all works OK. I have disconnected the compressor wires and it still blows. Any help on how to fix it would be great because the AZ heat is killer with no AC.

  • w3axxw3axx Posts: 2
    I just repaired a crazy, intermittent problem that I have been having for the past couple years with my 98 s10 wipers. I removed the cover of the wiper motor housing and pulled out the circuit board (was all rather easy to do) and found four bad solder joints on the board. Reheated those joints and applied a little solder and it is now working great. The joints that were bad were the ones to the connector to the wire harness ..... the largest tabs on the circuit board (probably the reason they were bad .... they didn't get heated enough in original manufacturing operation!!)
  • I had that problem last year and fixed it with a new wiper module from Autozone for about $25. My current problem is linked to the AC, Blower, or one of the parts in that system but I can't find it because it starts working when I trouble shot.
  • w3axxw3axx Posts: 2
    Wow! 25 bucks for a new module wasn't bad at all. I was feeling all "pumped up" cause I thought I saved myself from buying a $200 part !!!! ha ha ha The blower motor ...... hate those kinds of problems ... when they start working by the time you take it apart !! Be on the look out for bad solder joints (need a magnifying glass to see them) cause thats the way they often act up. GL
  • gonogogonogo Posts: 879
    Not bad solder joints, vibration problem.
  • oldtimer.....just curious if you've had any luck with your problem? I just got my S-10 back from the repair shop. It died out on me on the way home from work last week. I thought this was my electrical problem finally crapping out my computer. It turned out to be a bad catalytic converter. But since it was at the Chevy dealership I had them take a look at the electrical problem. Of course the answer they gave me was that the alternator was going bad. I know that's not the problem because I just put a brand new one in there. I had visions of them telling me it was 10 different things before it was ever fixed and me being out $2500! So I told them thanks, but no thanks and brought her home.
  • My AC electrical problem ended up being a bad compressor clutch or bad pressure switch I'm not sure which one or both but since the switch is in the back of the compressor I am replacing both to make sure.
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