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Amedee, Buick Mechanic
Category: Buick
Satisfied Customers: 24148
Experience:  ASE certified Technician advanced level specialist. Wisconsin certified emissions state inspector
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My 1991 Buick Lesabre sedan and the speedometer has quit. What

Customer Question

My 1991 Buick Lesabre sedan and the speedometer has quit. What is likely the cause and how do I repair it.
Submitted: 6 years ago.
Category: Buick
Expert:  Amedee replied 6 years ago.



WHat size engine do you have?


DO you have access to a scanner?

Customer: replied 6 years ago.
Yes I have a scanner, but the car is not where I am so, I cannot give you the engine size.
Expert:  Amedee replied 6 years ago.
DO you have a 4 cylinder or a v6?
Customer: replied 6 years ago.
Expert:  Amedee replied 6 years ago.

Scan the computer while driving and see if the vehicle speed shows up on the scanner.


Check for AC voltage back probed at the ECM between pins B10, a Yellow wire and B9 a Purple wire.

If the input to the ECM is OK, check for a good square wave output at pin B11, a Dark Green wire.

If the inputs to the ECM are correct and there is a good square wave output, verify a good wire between the ECM and the instrument panel cluster.

If OK, replace the cluster.


Potential Causes:

Electronic Control Module (ECM)
Instrument Panel Cluster (IPC)

Check for MPH in scan data.

Disconnect the Powertrain Control Module (PCM) 24 pin black connector, turn the key on, pulse the Green Vehicle Speed Sensor (VSS) output wire, pin B11 to ground.

The speedometer should move while this wire is pulsed to ground.

Test the Green wire from the PCM to the IPC for an open or short to ground.

Disconnect the cruise control module and the passive restraint module, check for voltage to return on circuit #389.


Potential Causes:


Circuit 389 - Open/short in the Green wire, circuit #389.


Customer: replied 6 years ago.
I thought you meant a scanner for loading pictures, etc. onto the computer. I do not have a car scanner.
Expert:  Amedee replied 6 years ago.
Check the AC voltage from the VSS sensor. If Ok, check the wiring... possible bad instrument cluster. If there is no AC voltage from the sensor, the sensor is bad and will need to be replaced.
Customer: replied 6 years ago.
Can you tell me how to identify these things? I checked and I cannot afford to buy this test equipment. How much can I expect to pay to have this work done and how much for the parts?
Expert:  Amedee replied 6 years ago.

Sorry for the delay!


Do you need the locations for the VSS sensor?


Do you have a voltmeter or a ohm meter?


Are you planning on bringing your vehicle into a small repair shop or the dealership?

Customer: replied 6 years ago.
Yes, I need the location of the vss sensor and I have a volt meter. I am not sure where I will take it; that's why I am asking how much I can expect to pay.
Expert:  Amedee replied 6 years ago.

The vehicle speed sensor is located Lower RH Rear Of Engine



Expert:  Amedee replied 6 years ago.
I would bet a shop would charge close to an hour to diagnose this problem. If you take it to a shop that charges 80 bucks an hour, then the diagnoses charge would be about 80 bucks plus tax.
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