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Codes in Drive, no codes in Overdrive


bvc

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Hello. I haven't found anything like this problem mentioned anywhere. It's a 91 cutlass supreme.

Driving in Overdrive yields no SES/codes and the car performs great.

Driving in third gear does. Codes 32 (EGR), 34 (MAP), 35 (IAC), and 44 (O2/lean), but the car performs great.

 

I just got the car a few weeks ago. The previous owner had the -random die/not start problem, and gave up after a new fuel pump, IAC, TPS, plugs/wires. I changed the CPS and knock sensor but it still died/no start. Changed the O2 sensor and fixed a vacuum leak and the car has been great. I drive 14 miles to work and can rarely get over 45. To prevent dropping into overdrive around (47/48mph) I prefer to drive in Drive and not have to jump back and for between Overdrive and 3rd gear. However, driving in 3rd gear yields all these codes, and I'm baffled. Could it be a transmission solenoid? I also don't know what this could mean for emission inspection coming in May. Thanks for any ideas and suggestions.

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that is a really odd combination of codes....

 

35 can only ever be set at idle(or if the ECM thinks it is at idle)

34 can only ever be set at a 700 or less RPM idle or with a throttle angle of 20% or greater and still reading full vacuum.

32 can only be tested while coasting down from a signficant speed with little/no throttle

44 can only be set when 33 or 34 aren't already set, closed loop is entered and O2 sensor voltage goes extremely lean for 60 seconds.

 

seems a lot of these are throttle related.

 

it's hard to diagnose further without scan data.

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Thanks. One time I removed the fuse to the ECM for a few minutes but the codes didn't clear. I guess that's still happening? Are they not supposed to clear on this car by removing the fuse to the ECM? I guess I need to disconnect the battery, make sure the codes are clear, then run it in drive again. Still don't understand why I would get the SES light in drive and not overdrive.

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there are two ECM fuses, the one you need to pull to clear codes is the one on the driver's side strut tower, in a little plastic box with the fuel pump relay. a couple seconds is all it takes.

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That explains that. I really need to get manuals for this thing. I have a 94 z24 j-body with the 3.1, but it's a little different.

Codes cleared. Just drove it and the SES light didn't come on. Before, I would get the SES light every time I put it in Drive and drove a few minutes.

Could the old codes have caused the light to come on in Drive and not Overdrive?

Edited by bvc
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the difference between the shifter being in D and OD shouldn't change SES operation. codes cause it to come on regardless.

 

i want to say history codes won't make it come on, only current ones. so if it was setting codes in the last drive cycle, but doesn't the next time, the light would stay off.

 

it's been so long since i've had a code get set on a GM OBD1 vehicle that i've forgotten the exact process the ECM goes through to trigger the light.

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