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Shifting Problems After Coolant Change

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Shifting Problems After Coolant Change

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Old 02-10-2018, 12:22 AM
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Shifting Problems After Coolant Change

2009 LS1 85K miles.

I had the coolant changed today. On the way home the engine didn't sound as it usually does, but I didn't think much of it. After driving about an hour this evening, it has developed shifting trouble and the CEL is on.

My scanner reads four fault codes:

P0700 (Transmission Control Module Requested MIL Illumination-I assume this turns on the CEL) and

P0700 Pending

And two "N/A".

Any ideas? Is the coolant change just coincidence?
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Old 02-10-2018, 07:56 AM
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Seems a wire got knocked loose or broken





Check the ground wire at the stud on the transmission case to the right of the oil filter housing
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Old 02-10-2018, 08:27 AM
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Thanks, Blue, I'll check that.
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Old 02-10-2018, 08:32 AM
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The coolant change has nothing to do with it, but sloppy workmanship does.

If they somehow managed to touch the TCM case with a hot wire the TCM is fried. More likely they jiggled wires while fidgeting with the t-stat. The transmission electrical connector is in that area.
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Old 02-10-2018, 10:34 AM
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Thanks Don. I don't see any wires off. I drove about a half hour each way on the Parkway (70-75 mph) while out and didn't have any trouble until a few minutes after I got off the highway. At a traffic light, it would rev up before getting going and the like.

It sat for two and half weeks while I was away until last week. I did notice it was a little sluggish starting a few times, but it seemed to clear up after a few days.
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Old 02-10-2018, 11:18 AM
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A couple other thoughts... have your battery tested, post up voltage/amperage results here. A dying battery can cause strange problems.

Have someone with a better scanner check for codes. P0700 is very generic, there may be more specific codes hiding in there.
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Old 02-10-2018, 11:41 AM
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Thanks, RJ. I just went out to try it. I don't have Reverse; it's just like it's in Neutral. It creeps a little in Drive, but I only have a few feet to the front of the driveway, so I don't want to go further. I noticed a chemical smell around the car, faintly like mothballs.

When I stopped at the store on the way home last night, I now recall Reverse was "slipping" but then engaged. I didn't leave it in Reverse long. It was also giving me shifting problems at that time.

I just rescanned; I got the generic P0700 and P0700 Pending but those were the only Faults; the N/A no longer appears. BTW, the scanner is an Autel MS300.
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Old 02-10-2018, 03:01 PM
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P0700 is a communication problem from the transmission to the TCM, because of the possibility of wires getting moved around and dislocated whilst changing the thermostat, look in that area. Wires don’t look broken but can be every so slightly disconnected. Physically check the TCM wire harness, the harness goes to the transmission. And then try the good old battery lobotomy, disconnect the negative terminal at the battery, DO NOT close the rear lift gate, put a folded towel in the latch to avoid accidental closing.
Check the fuse block for loose halves, loose fuses, loose relays, inspect and clean under hood ground wires. Reconnect the battery negative terminal ( about 30 minutes should have passed by now), start up the HHR. Hopefully that be that, if not you’ll need a scanner that can read transmission codes per
https://www.obd-codes.com/p0700
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Old 02-10-2018, 03:10 PM
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Thanks, I'll give a look.

Well, looks like a lot of rain the next two days, so I guess I won't get much done; I don't have a garage and have to work outside.

Last edited by SlickRick2; 02-10-2018 at 03:40 PM.
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Old 02-11-2018, 04:13 PM
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Still pouring rain! I think it might be best to flatbed it to the local trans. shop. I think they are reliable; they've been there for 30 years. I'll be away starting next Saturday until the end of the month, but I'll keep you posted on what happens.
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