1993 Cadillac DeVille High Idle Speedometer Fix

GMC
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TANYAK
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  • 3 POSTS
I HAVE A 93 DEVILLE 139,000 MILES ON IT AND I HAVE BEEN HAVING SOME PROBLEMS. whenever the service engine light is on (not the service vehical light) the car itels at 3000 RPMS and the spedometer stops working and it wont be in the right gear that it should be in, but once that light shuts off the car runs fine it itels fine and the spedometer works. i replaced the transmission and the TPS and its still having problem please help me!!!
Mar 28, 2006 at 12:53 PM
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KENB79764
  • ✓Experienced Mechanic
  • 52 POSTS
sounds like the vehicle speed sensor may be going bad. it will cause the computer to put the car into a limp mode.
Apr 5, 2006 at 2:55 AM
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TANYAK
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[quote:599704521d="kenb79764"]sounds like the vehicle speed sensor may be going bad. it will cause the computer to put the car into a limp mode.[/quote:599704521d]

Is that going to cost a fortune?, i just ran another self diagnostic on it and it ran a code for loss comunication from the ECM to the BCM
Apr 8, 2006 at 5:42 AM
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KENB79764
  • ✓Experienced Mechanic
  • 52 POSTS
the speed sensor is usually under forty dollars depending on the vehicle. it may be slightly more on your caddy. it is just an electronic sensor that mounts in the transmission. it is normally about an hour to install.
Apr 9, 2006 at 1:11 AM
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TANYAK
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[quote:e735771720="kenb79764"]the speed sensor is usually under forty dollars depending on the vehicle. it may be slightly more on your caddy. it is just an electronic sensor that mounts in the transmission. it is normally about an hour to install.[/quote:e735771720]

it wasnt the sensor but i put in a new ECM and that was the problem , thanks for your help. i appreciate it
Apr 14, 2006 at 9:22 AM
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Suggested Repair

Symptoms point to limp mode. The vehicle speed sensor was suggested (often under about $40 and about an hour to install in the transmission), but the owner reported a loss-of-communication code from the ECM to the BCM and confirmed that replacing the ECM fixed the problem.

Conversation Summary

A 1993 Cadillac DeVille with about 139,000 miles idled near 3000 RPM, lost speedometer function, and shifted incorrectly only while the service engine light was on, then ran normally when the light went out. The transmission and TPS had already been replaced. An expert suggested a failing vehicle speed sensor causing limp mode. A self-test later showed loss of communication from the ECM to the BCM, and the owner confirmed a new ECM resolved the issue.

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