downshift switch malfunction?
litlred
10-01-2005, 06:16 PM
1999 Chevy s10 4wd, automatic transmission.
'Service Engine Soon' light came on a couple weeks ago; keep it regularly serviced, so we had the transmission fluid changed...new filter, etc. Looked good...no burnt smell, very little debris. Truck showed a little hesitation on starting out, but then would shift smoothly. If we stopped for a few moments, and shut it off, it would run perfectly. Behaved itself for a week after the fluid change.
Light came on and stays on and now truck basically will not shift down from overdrive or 3rd to lower gears. You can manually put the transmission in Rev, 1st, 2nd or 3rd just fine, but it won't shift on its own. Shifting is pretty smooth...doesn't appear to be any trouble with the actual transmission.
We'd use the diagnostic computer, but somewhere there is a power failure to the diagnostic port... (main computer has power to it), so we can't get a computer readout for a problem.
Someone suggested to us it could very well be a 'downshift switch' located under the steering column in the dash.
Has anyone had any experience with one of these going out...or possibly another relay or solenoid we might be overlooking?
Getting desperate! Thanks in advance for any replies!!
'Service Engine Soon' light came on a couple weeks ago; keep it regularly serviced, so we had the transmission fluid changed...new filter, etc. Looked good...no burnt smell, very little debris. Truck showed a little hesitation on starting out, but then would shift smoothly. If we stopped for a few moments, and shut it off, it would run perfectly. Behaved itself for a week after the fluid change.
Light came on and stays on and now truck basically will not shift down from overdrive or 3rd to lower gears. You can manually put the transmission in Rev, 1st, 2nd or 3rd just fine, but it won't shift on its own. Shifting is pretty smooth...doesn't appear to be any trouble with the actual transmission.
We'd use the diagnostic computer, but somewhere there is a power failure to the diagnostic port... (main computer has power to it), so we can't get a computer readout for a problem.
Someone suggested to us it could very well be a 'downshift switch' located under the steering column in the dash.
Has anyone had any experience with one of these going out...or possibly another relay or solenoid we might be overlooking?
Getting desperate! Thanks in advance for any replies!!
maxwedge
10-01-2005, 06:41 PM
No downshift switch here all done by pcm, check your liter fuse this will power up the scanner, get codes and post back.
litlred
10-01-2005, 08:37 PM
No downshift switch here all done by pcm, check your liter fuse this will power up the scanner, get codes and post back.
Thanks so much for your fast reply: I am SO automotive illiterate. I read your reply, and it took awhile to sink in. My nephew was testing some of the fuses, and found a dead 15amp fuse that went to the cigar lighter. We never thought it would have anything to do with the computer port. We'll replace the fuse tomorrow and try to get someone with a diagnostic computer to try again.
The PCM you mention...performance control module? Is this located beneath the steering wheel column in the dash?
I really appreciate your help...any other suggestions you might have would be greatly appreciated! This forum is a blessing and we appreciate folks like you that take the time to help people like us!!!
Thanks so much for your fast reply: I am SO automotive illiterate. I read your reply, and it took awhile to sink in. My nephew was testing some of the fuses, and found a dead 15amp fuse that went to the cigar lighter. We never thought it would have anything to do with the computer port. We'll replace the fuse tomorrow and try to get someone with a diagnostic computer to try again.
The PCM you mention...performance control module? Is this located beneath the steering wheel column in the dash?
I really appreciate your help...any other suggestions you might have would be greatly appreciated! This forum is a blessing and we appreciate folks like you that take the time to help people like us!!!
blazee
10-01-2005, 08:52 PM
PCM stands for Powertrain Control Module. Your's is located on the passenger side fender, mounted on the coolant reservoir.
Your transmission is acting like that because it is in "limp mode". When certain problems occur... a trouble code is stored, the SES light comes on, and the PCM sets the tranny to "limp mode" to minimize damage and allow you to get to safety.
There is some info here that tells you the codes and the default action that occurs when they are set:
http://www.automotiveforums.com/vbulletin/showthread.php?p=3202213
Finding out the codes that are set on your truck will help to identify the problem. Autozone will read them for free.
Your transmission is acting like that because it is in "limp mode". When certain problems occur... a trouble code is stored, the SES light comes on, and the PCM sets the tranny to "limp mode" to minimize damage and allow you to get to safety.
There is some info here that tells you the codes and the default action that occurs when they are set:
http://www.automotiveforums.com/vbulletin/showthread.php?p=3202213
Finding out the codes that are set on your truck will help to identify the problem. Autozone will read them for free.
litlred
10-01-2005, 09:45 PM
Thank You for taking the time to reply; this site is the best one we've ever found~we're going to 'limp' into autozone tomorrow, replace that fuse, hope their computer will read our truck's woes and go from there. Thanks to everyone!!!
rlith
10-02-2005, 06:50 AM
Just a note. The cigarette lighter fuse doesn't have anything to do directly with the computer. The issue is that the code reader gets it's power from the cigar lighter typically (typically, depends on the model, some pull power directly from the aldl) So more than likely it was connecting simply because the reader couldn't get power from the lighter..:) Just thought I'd throw that in.
But people here are correct. Get the code 1st, we can help you better that way.
But people here are correct. Get the code 1st, we can help you better that way.
litlred
10-02-2005, 08:45 AM
Went to Autozone again...bought a 15amp fuse and installed it in the cigar lighter fuse slot...SUCCESS...the obd was reading like crazy and flashing a bunch of error codes which include:
P0740, P0753, P0758, P1860, P1810, plus he wrote down:
TCC Circuit Malf., Shift Solenoid A circuit mal., Shift Solenoid B circuit malf., Shift/timing solenoid mal., manufactuer contrl. trans.
He suggested a PCM replacement, and scared us with a very high priced replacement estimate...but they don't carry that module.
Truck is in 'limp mode'...we carefully drive it on the backroads and manually shift it from 1st up so as not to force it to labor up the hills and going from a stop.
Another forum member suggested it might be a problem with the ignition switch....any other symptoms here that we might look for to indicate this?
We appreciate any and all advice since we are pretty amateur regarding anything computer related in automotive~thanks in advance for your time and advice!
P0740, P0753, P0758, P1860, P1810, plus he wrote down:
TCC Circuit Malf., Shift Solenoid A circuit mal., Shift Solenoid B circuit malf., Shift/timing solenoid mal., manufactuer contrl. trans.
He suggested a PCM replacement, and scared us with a very high priced replacement estimate...but they don't carry that module.
Truck is in 'limp mode'...we carefully drive it on the backroads and manually shift it from 1st up so as not to force it to labor up the hills and going from a stop.
Another forum member suggested it might be a problem with the ignition switch....any other symptoms here that we might look for to indicate this?
We appreciate any and all advice since we are pretty amateur regarding anything computer related in automotive~thanks in advance for your time and advice!
blazee
10-02-2005, 04:38 PM
As GMMerlin said, those codes indicate a loss of power to the tranny and it typically is the ignition switch that causes the loss of power.
Another symptom that sometimes occurs is ocassional erratic gauge and a dash light operation.
With the switch on, check for voltage at fuse #11 (cluster). If no voltage or low voltage is present, then I would suspect the ignition switch (or faulty wiring for a remote starter if you have one)
If you have voltage there, try turning the switch on and off a few times to make sure that it remains constant.
If the voltage is present and stays constant, then inspect the wiring going to the transmission.
Another symptom that sometimes occurs is ocassional erratic gauge and a dash light operation.
With the switch on, check for voltage at fuse #11 (cluster). If no voltage or low voltage is present, then I would suspect the ignition switch (or faulty wiring for a remote starter if you have one)
If you have voltage there, try turning the switch on and off a few times to make sure that it remains constant.
If the voltage is present and stays constant, then inspect the wiring going to the transmission.
litlred
10-02-2005, 05:29 PM
Many thanks to maxwedge, rlith and Blazee; don't know what we'd do without you! We'll take your advice and see what happens~and keep posted on results...thanks again for your help!
blazee
10-02-2005, 05:33 PM
To see GM's bulletin on the ignition switch issue, see problem 3 of this thread:
http://www.automotiveforums.com/vbulletin/showthread.php?t=461182
http://www.automotiveforums.com/vbulletin/showthread.php?t=461182
maxwedge
10-02-2005, 06:37 PM
Blazee, again on the money here, great advice/help, on target.
blazee
10-02-2005, 08:02 PM
Blazee, again on the money here, great advice/help, on target.
Thanks, it's always nice to get positive feedback. I've seen you giving a lot of good advice, too. I hope that you will stick around a while.
Thanks, it's always nice to get positive feedback. I've seen you giving a lot of good advice, too. I hope that you will stick around a while.
bigbutr
12-20-2005, 05:53 PM
Situation in a nutshell:
Work for the USPS doing a rural route with a 1996 S-10 Ext Cab with the 4.3. Delivering mail in the woods, went through a large rut filled with water that sucked some into the engine stallilng it out. Got it towed back, pulled the plugs, wires and drained the water out completely. Also changed the oil. Luckily, engine fired up after all that and runs smoothly.
Went to drive it the next day and the tranny started acting up. Got up to speed and it started fluctuating out of OD and drive.
Took it to the local AAMCO shop and when I talked to them, they said a bunch of codes came up and that it was going to take 'hours' of diagnostics to figure out all of it.
I read where you were talking about ignition switch problems causing tranny issues and I'm wondering if that might be my problem as well. I don't want to tell AAMCO how to do their jobs, but then I don't want to get shafted out some bucks for a new PCM ($800 was what he said) if I don't really need one. Not that I'm trying to be cheap, but I'm not wanting to pay someone's big Xmas bonus either.
Is it likely something went wrong with the ignition switch? The truck did not stay submerged since I made it through the water. I guess I need to get the codes to find out for sure.
Thanks for any assistance you can offer
Steve
Work for the USPS doing a rural route with a 1996 S-10 Ext Cab with the 4.3. Delivering mail in the woods, went through a large rut filled with water that sucked some into the engine stallilng it out. Got it towed back, pulled the plugs, wires and drained the water out completely. Also changed the oil. Luckily, engine fired up after all that and runs smoothly.
Went to drive it the next day and the tranny started acting up. Got up to speed and it started fluctuating out of OD and drive.
Took it to the local AAMCO shop and when I talked to them, they said a bunch of codes came up and that it was going to take 'hours' of diagnostics to figure out all of it.
I read where you were talking about ignition switch problems causing tranny issues and I'm wondering if that might be my problem as well. I don't want to tell AAMCO how to do their jobs, but then I don't want to get shafted out some bucks for a new PCM ($800 was what he said) if I don't really need one. Not that I'm trying to be cheap, but I'm not wanting to pay someone's big Xmas bonus either.
Is it likely something went wrong with the ignition switch? The truck did not stay submerged since I made it through the water. I guess I need to get the codes to find out for sure.
Thanks for any assistance you can offer
Steve
litlred
12-20-2005, 08:13 PM
Hi Steve, and welcome to AF...the folks here are the most helpful bunch you'll ever meet...trust their advice!
We posted the PCM thread and the downshift mod thread in an effort to determine what our truck was doing after the 'check engine' light came on and stayed on~our trouble codes we got are posted on the PCM thread.
I don't know what kind of troubles your transmission is pulling: getting the codes is really important and you'll get your best advice if you have them to post on this forum.
Our 1999 S10 Zr2, 4.3 wasn't hitting 1st or overdrive; the guys told me that it was staying in 'limp mode' as a safety measure to protect the transmission and that it most likely was an electrical issue.
We had the transmission serviced and changed the filter...fluid was nice, red and clean...
After a 'reputable' tranny shop wanted to do a $1200 rebuild and claimed it was the front forward clutch, we finally found an honest tranny man. (after limping around for nearly 2 weeks)
It turned out to be Shift Solenoid A, Shift Solenoid B and another switch that was loose...all in the transmission fluid pan area: $200 later we were on our way.
Get the codes and start a new thread with your question, and I'm sure you'll get the help you need...we did! :grinyes:
We posted the PCM thread and the downshift mod thread in an effort to determine what our truck was doing after the 'check engine' light came on and stayed on~our trouble codes we got are posted on the PCM thread.
I don't know what kind of troubles your transmission is pulling: getting the codes is really important and you'll get your best advice if you have them to post on this forum.
Our 1999 S10 Zr2, 4.3 wasn't hitting 1st or overdrive; the guys told me that it was staying in 'limp mode' as a safety measure to protect the transmission and that it most likely was an electrical issue.
We had the transmission serviced and changed the filter...fluid was nice, red and clean...
After a 'reputable' tranny shop wanted to do a $1200 rebuild and claimed it was the front forward clutch, we finally found an honest tranny man. (after limping around for nearly 2 weeks)
It turned out to be Shift Solenoid A, Shift Solenoid B and another switch that was loose...all in the transmission fluid pan area: $200 later we were on our way.
Get the codes and start a new thread with your question, and I'm sure you'll get the help you need...we did! :grinyes:
bigbutr
12-20-2005, 08:32 PM
Thanks for the advice. I usually do most of the work on the vehicle, but this one seems a little out of my league. I just have a problem with a 'reputable' nationwide shop saying we'll start with three hours of diagnostics and then go from there. As if I have a ton of money, especially this time of year.
I plan on going and getting the truck in the morning and bringing it home and trying to go some cleaning. The puddle I ran through was muddy and there is a lot of residue all over the engine compartment and underneath as well.
Hopefully they won't be a pain about giving me the codes, but if they do, I'll just go across the way to Autozone and get them to give them to me.
Again, thanks and I look forward to being a longtime member of this forum.
Steve
I plan on going and getting the truck in the morning and bringing it home and trying to go some cleaning. The puddle I ran through was muddy and there is a lot of residue all over the engine compartment and underneath as well.
Hopefully they won't be a pain about giving me the codes, but if they do, I'll just go across the way to Autozone and get them to give them to me.
Again, thanks and I look forward to being a longtime member of this forum.
Steve
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