Freaky Speedometer
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Cargo Master
Joined: Jul 2006
Posts: 2,756
Likes: 38
From: Nampa, ID
Freaky Speedometer
On the way home from work tonight, my speedometer quit. I mean quit; needle dropped to the zero peg, odometer blanked out. Everything else worked. Tach was reading 2K, all other guages were fine. OD light did not flash. I checked for codes anyway. None.
I'm wondering if the speedometer unit (PSOM?) is the culprit and is causing my phantom P0500 codes.
I guess I'm gonna hafta remove the instrument cluster, if it can be tested somehow.
Anyone have any ideas on what else I need to consider as a possible culprit?
The CPS and VSS are two to three months old. The new CPS seems to have kept the "CMP Intermittent Error" from reappearing, so I think the recall CPS was going bad.
Haven't had a P0500 code in a few weeks, but the speedometer unit is acting up worse than ever.
This is really frustrating and I'm not sure how to fix this. Please send ideas.
I'm wondering if the speedometer unit (PSOM?) is the culprit and is causing my phantom P0500 codes.
I guess I'm gonna hafta remove the instrument cluster, if it can be tested somehow.
Anyone have any ideas on what else I need to consider as a possible culprit?
The CPS and VSS are two to three months old. The new CPS seems to have kept the "CMP Intermittent Error" from reappearing, so I think the recall CPS was going bad.
Haven't had a P0500 code in a few weeks, but the speedometer unit is acting up worse than ever.
This is really frustrating and I'm not sure how to fix this. Please send ideas.
Hotshot
Joined: Jul 2003
Posts: 12,177
Likes: 40
From: Newport, WA
Craig, 90% sure your PSOM just went TU on you. The only good way to test it is to swap in a cluster from another similar truck and see if the problem goes away. For testing any year PSD will do, but for a permanent fix you'll want another 97 cluster because there are small wiring differences among the years. You can get used clusters fairly cheap, around $40 or so. I think, but can't say for sure, that the PSOM is the same between gas and diesel and among years so if you end up with a gasser cluster or one that's not from a 97 you can disassemble both clusters and swap the PSOM/speedo unit over. Just remember that whatever mileage the donor rig had will now show on your truck... PSOM stores mileage. When the PSOM quit in my 95 I dug around quite a bit and found a cluster on Ebay that was within 200 miles of what was on my truck, cost me $125 but worth it to me.
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Cargo Master
Joined: Jul 2006
Posts: 2,756
Likes: 38
From: Nampa, ID
All good info, guys. Thanks.
Madpoque, the odometer blanks out when the speedo stops working, but when the speedo starts working again, the mileage has increased.
Action4478, what part of the wiring went bad? What am I looking for? There's no visible abrasion, cracking or tears in the insulation or wiring near the connector. My truck has a 168" wheelbase. That's a lot of wiring to look at. Did a particular location rub through?
Superduty4x4, mcdavidson is a funny guy, isn't he? I was afraid it might be the PSOM. I asked my dealer if they were available and was told they are now obsolete and unavailable. eBay or the "Pick-and-Pull", here I come.
Mcdavidson, Veerrry funny. Thanks again for the help with the GPR "testing". PEBWAP, huh...is that like a "keyboard" issue causing computer problems?
96ExtracabPSD, I don't think it's a fuse. The tranny works fine when this happens AND the speedo/odo start working again.
I guess I'm gonna hafta crawl under the truck and start looking.
Madpoque, the odometer blanks out when the speedo stops working, but when the speedo starts working again, the mileage has increased.
Action4478, what part of the wiring went bad? What am I looking for? There's no visible abrasion, cracking or tears in the insulation or wiring near the connector. My truck has a 168" wheelbase. That's a lot of wiring to look at. Did a particular location rub through?
Superduty4x4, mcdavidson is a funny guy, isn't he? I was afraid it might be the PSOM. I asked my dealer if they were available and was told they are now obsolete and unavailable. eBay or the "Pick-and-Pull", here I come.
Mcdavidson, Veerrry funny. Thanks again for the help with the GPR "testing". PEBWAP, huh...is that like a "keyboard" issue causing computer problems?
96ExtracabPSD, I don't think it's a fuse. The tranny works fine when this happens AND the speedo/odo start working again.
I guess I'm gonna hafta crawl under the truck and start looking.
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Lead Driver
Joined: Oct 2003
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From: Madison, WI
If it were the other way around, that is, the VSS -> PCM connection were bad, but the PCM -> dash connection were good, I would expect the odometer to keep showing a number, but for the number not to change (IOW, the PCM thinks the truck is not moving). I would also think that if the VSS -> PCM connection were bad, you'd have shifting problems.
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Hotshot
Joined: Aug 2006
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Action4478, what part of the wiring went bad? What am I looking for?
I hooked up my scanner & went for a drive ,ironically , I drove down a fairly bumpy road ,,after a short drive I noticed the spedo dropping to O nearly at every bump..
The drive home from the auction where I bought it ,,the tires were severly out of balance ,,I noticed it then too,,
I took a couple of weeks to find the problem
Hotshot
Joined: Aug 2006
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Action4478, what part of the wiring went bad? What am I looking for?
I bought a used assembly for $100.00 on car- part .com
Hotshot
Joined: Jul 2003
Posts: 12,177
Likes: 40
From: Newport, WA
Craig- does the speedo bounce at all, or does it just quit? If it just plain quits it might be wiring like Rick said. When my PSOM quit me, it quit me once going down the freeway between Twin and Boise... just flat quit for a few miles then sprang back to life after I thumped the dash a few times. Went along fine for a week or so, then I started getting a bouncing speedo, and I mean REALLY bouncing- would go from 40 to 70 at around 65 mph. Definitely check the wiring before you go spending $ on parts. It also wouldn't hurt to pull the VSS out and wipe it off to see if that helps.
Lead Driver
Joined: Oct 2003
Posts: 8,476
Likes: 37
From: Madison, WI
But if the odometer is still accumulating, even with the speedo/odo not working, the VSS must be working, right? Do any of the scanners, chips, scangauges, etc., read real-time speed? It'd be interesting to plug one into the diagnostic connector, to see if it still reads road speed even when the speedo on the dash fails.
Lead Driver
Joined: Oct 2003
Posts: 8,476
Likes: 37
From: Madison, WI
But I'll bet when you got yours fixed, the odometer didn't account for the interim miles driven, right? THAT's the key. The OP said when her/his odo came back, the mileage had increased. That indicates a good signal from the VSS to the PCM (I THINK).