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transmission/speedometer/service engine soon


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My '98 Deville Concourse service engine soon light is on solid. Sometimes, I can feel the transmission have a hard time getting into 4th gear. After this happens once, the speedometer is erratic. Other times, the transmission shifts normally and the speedometer works fine. The car has 88,000 miles and has never been worked hard. From what I've read this may be a solenoid problem. I"m going to check for codes. Any other suggestions on what I can check?

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Turn the key to the "ON" position and simultaneously hold down the OFF and WARMER buttons on the heater controls. You should be able to read the codes that correspond to the problem(s) that turned the light on. Write them down and post them back here. Someone should be able to take you further at that point.

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The Service Engine Soon Light was on for about two weeks while the transmission problem was occurring. After I checked for codes the light went out. No codes were found and I swear I didn't clear any codes.

For the last week, the speedometer has not been erratic at all. The transmission, on the other hand is still not going into high gear. The tach reads over 2500 rpm at about 65 mph and it sounds like it's in third gear. This problem does not happen all of the time. Usually, when I first take the car out, the transmission works fine. The problem starts after about 20-30 minutes of driving. Since I looked for codes, the service engine soon light has not returned.

I've noticed that when the transmission problem is occurring, the cruise control doesn't work. When the transmission is operating normally, the cruise control works normally also.

On three occasions when the transmission was not working properly, I put my foot on the brake while holding the accelerometer steady. In all three tests, I did not see any jump in rpm. I repeated the test when the transmission was working normally and got a bump of about 50-100 rpm.

One other thing that's strange.... When I shut off the car I hear a "psssstttt" of air (I suppose). It only lasts a second. Today, I heard a longer, slower release of air that lasted about 3 seconds. The sound seems to come from the passenger side in the vicinity of the rear door. I don't remember this noise previously.

1. Could the erratic tachometer problem that has not returned been caused by snow/ice buildup around the wheel speed sensors?

2. Could the transmission problem I've described be a result of a plugged screen or vacuum problem?

I work out of state and am only home part of the weekend. I hate to just leave the car at a dealership or repair shop without more insight about the problem. Previous experience in situations like this has resulted in a recommendation of replacing the transmission. I don't thing that is necessary in this case. Any further ideas?

One last bit of information.... I did have the transmission flushed. That was before I came to this site and read the warnings against fulshing. I had the transmission flushed during the time that the service engine soon light was on and the tachometer was erratic. Nothing changed after the flush. It was another two weeks before I checked codes and the service engine light went out.

Thanks in advance for your help.

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I'm betting the air release sound you are hearing is from the ELC venting when you shut it down. I have heard that on occasion. Normal condition I believe.

I am no trans expert but from what I have read on this site is kinda sounds like shift solenoids. Be careful. You wouldn't be the first one on this board that was told he needed an new trans when solenoids where all that was needed. The flush is the wild card and scary part.

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Not shifting into 4th and no cruise control sounds like the brake pedal switches are closed. Try lifting the pedal up with your toe.

Or start the car and walk around to see if your brake lights are on.

Good luck.


Drive your car.

Use your cell phone.


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  • 2 weeks later...

98 Deville Concourse

An update on this intermittent transmission problem.......

Yesterday, the Service Engine Soon light came back on while my wife was driving. She felt the car hesitate....no power....then normal operation. I checked for codes when she returned and found none.

Today, the light was still on with no codes. The car drove fine for a while then I felt the hesitation while I was driving. I observed the following:

1. Error code PO503 (Vehicle Speed Sensor VSS circuit intermittent)

2. Higher than normal engine speed

3. Cruise control not functioning

I shifted out of overdrive into 3rd gear for a few minutes then back into overdrive. The problem was gone and the car was driving normally. I cleared the PCM code and the service engine light went away.

Where is the vehicle speed sensor located?

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