2001 GMC Safari Intermittent Upshift Failure

Tiny
RMOP
  • MEMBER
  • 2001 GMC SAFARI
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 59,000 MILES
Every few months, we drive our Safari outside of the city. And, for the past 6-9 months (est), I've noticed upshift failures on such high-speed (70mph) excursions.

Initially, only the Overdrive was affected. At that time, I dutifully checked my fluid level with the engine fully warm. It was fine, color was red and clear, and there was no odor.

Today (a few weeks after my last excursion), it didn't initially shift out of 2nd gear, though eventually did so. I don't believe it ever went to OD.

Shifting (at least between 1st & 2nd) is smooth and quiet. The transmission engages immediately in both forward and reverse, and there is no slippage or noise.

After today's trip, I re-checked the fluid, and it remains fine.
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Wednesday, June 10th, 2009 AT 3:38 PM

7 Replies

Tiny
DOCFIXIT
  • EXPERT
Hi
Possible faults speed sensor, input or output speed sensors and shift solenoids. To know for sure need the transmission diagnosticaly scanned. Let me know results and will advise.
Thanks for donate
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Thursday, June 11th, 2009 AT 9:05 AM
Tiny
RMOP
  • MEMBER
NOTE: I live in the UK. This is an American-version vehicle shipped privately to the UK. The mechanic's shop was busy but unusually well-ordered and tidy. The mechanic himself seemed competent. He did NOT charge me for the diagnosis which he was unable to provide via computer. He did perform a road test at highway speeds.

Diagnostic scanning was unsuccessful. Mechanic said that he suspected the problem was with one or more Shift Control Modules and/or Speed Sensors. He was perplexed that there was no diagnostic output to his instrument, but indicated that there should also have been some sort of fault code sent to the vehicle's dash disply. There was not.

Mechanic suggested two options:

1) remove pan and examine things visually and remove and test the associated electronics to find the faulty component(s). This would cost about 200, with no guarantee that it would correctly identify the problem. Fixing it would be more.

2) replace the entire transmission with a NEW one which I provide, as he fears diagnosis and replacement of faulty sensors, etc. Is going to get pricey enough to justify considering a replacement. He could get one in the UK, but indicated I could probably do much better on price with US contacts, etc. Than could he.

Can you actually GET a NEW transmission? If so, where? And for how much?

Thanks.
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Thursday, June 18th, 2009 AT 5:49 AM
Tiny
DOCFIXIT
  • EXPERT
Are there any GM dealers in U.K? If yes go there for diagnosis if no not sure what to suggest. Does this Tech have GM experience? If no can you find shop that does? Yes you can get a new trans from GM most choise a remanufactured unit. Approxmit cost $3000.00 plus shipping
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Thursday, June 18th, 2009 AT 10:23 AM
Tiny
RMOP
  • MEMBER
No GMC dealer located in London (yet). I took the Safari to another transmission shiop. Using a different diagnostic box, he also failed to get any codes from the transmission, though could get them from the engine itself. This mechanic drove me around the block to yet another mechanic who (it was obvious) works on ONLY American-built cars. Using a third diagnostic box, he also failed to get any meaningful output regarding the transmission.

Both expressed the opinion that I had two bad control modules, and suggested dropping the pan and checking them manually. The tranmision mechanic expresed optimism that the hydraulics and mechanics of the transmission are probably intact.

I asked if it made sense to replace all FOUR sensors (in two in fact prove bad) while the transmission is open -- he said he'd be happy to do so, but didn't seem to think it necessary. I thought, while this thing is open.

Anything else I should have them check/replace while it's open? They mentioned changing the fluid, the screen and the gasket. Anything else in there a "must do" while it's open?

Many thanks.
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Tuesday, July 7th, 2009 AT 4:05 AM
Tiny
DOCFIXIT
  • EXPERT
Can you post the engine codes the Tech got. In P0XXX format. Engine codes can cause shift to be inaccurate.
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Tuesday, July 7th, 2009 AT 1:33 PM
Tiny
RMOP
  • MEMBER
Well, it was already in the shop by the time I read your post. FINDING: Nothing. Everything inside looked fine, and all of the sensors read fine, and compared exactly with new ones which had been obtained to replace them. The old ones were retained, and the mechanic is stumped. But clearly honest. I'm out 80 for the labor and parts to drop the pan, inspect, and refill the transmission.

As to engine codes, the only one indicated a misfire on one (1) cylinder, number six (6), I believe. Over the phone, he didn't seem familiar with the request for a download to a POXXX format file. I'll check again.

He mentioned some possible issues with information from the engine throttle not being properly communicated. But, it's clearly over his head at the moment.

Thanks.
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Wednesday, July 8th, 2009 AT 7:26 AM
Tiny
DOCFIXIT
  • EXPERT
Spo trans checked out good but still have problem correct? You think Techs at shop would communicate with me via internet? If so that maybe the solution.
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Wednesday, July 8th, 2009 AT 8:04 AM

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