Faulty Tachometer

[blackaurora35]

Hi aurora fans...
My 01 black aurora is running fine but the tachometer has been erratic lately. While driving normally it suddenly jumps up to 8000rpms and stays there. The engine is running normally during this episode. When the tach starts to work again it seems to run in a range much higher than the actual enigine speed. I am not noticing any problems with the engine or transmission - no lurching or anything like that. Turning off the ignition and restarting seems to reset everything temporarilly.
I am thinking a sensor or faulty wiring. Anybody with similar experiences....

[Superdemon]

My guess would be a grounding issue.

[Marc]

Troubleshooting procedure from the 2001 shop manual for this problem.......................................................................................

[aurora2001tan]

Revised version

SMU - Revised Speedometer and/or Odometer Innacurate or Inoperative, Tachometer Inaccurate or Inoperative Symptom Charts #01-08-49-019
Revised Speedometer and/or Odometer Inaccurate or Inoperative, Tachometer Inaccurate or Inoperative Symptom Charts
2001 Oldsmobile Aurora

This bulletin is being issued to revise the Speedometer and/or Odometer Inaccurate or Inoperative symptom chart. A test description has been added and Step 5 of this chart has been revised. Also revised is the Tachometer Inaccurate or Inoperative symptom chart. A test description has been added and Step 4 of this chart has been revised. Please use the following to replace the existing information in the Instrument Panel and Console sub-section of the Service Manual.

This information has been updated. If you are using a paper version of this Service Manual, please mark a reference to this bulletin on the affected page in the Instrument Panel and Console sub-section of the Service Manual.

Speedometer and/or Odometer Inaccurate or Inoperative
Test Description
Step 5. This step tests the complete vehicle speed signal circuit from the PCM to the cluster, including the flat wire harness C215 to the IPC. For more information on flat wire circuits refer to Inline Harness Connector End Views in Wiring Systems.

Step
Action
Yes
No

Schematic Reference: Instrument Cluster Schematics

1
Did you perform the Instrument Cluster Diagnostic System Check?
Go to Step 2
Go to Diagnostic System Check -- Instrument Cluster

2
Install a scan tool.
Raise the vehicle drive wheels. Refer to Lifting and Jacking the Vehicle in General Information.
Start the engine.
Place the transmission into drive.
With a scan tool, observe the Vehicle Speed Sensor parameter in the PCM Engine Data 1 list.
Does the Vehicle Speed Sensor parameter match the speedometer display?
Go to Step 3
Go to Step 4

3
Does the odometer work properly?
Go to Testing for Intermittent and Poor Connections in Wiring Systems
Go to Step 9

4
Turn the ignition OFF.
Disconnect the PCM connector C1.
Turn the ignition ON, with the engine OFF.
Measure the voltage from the vehicle speed signal circuit to a good ground.
Does the voltage measure greater than 9.0 volts?
Go to Step 6
Go to Step 5

5
Test the vehicle speed signal circuit for an open, for a short to ground, or for a high resistance. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?
Go to Step 12
Go to Step 7

6
Test the vehicle speed signal circuit for a short to battery. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?
Go to Step 12
Go to Step 8

7
Test the ignition 1 voltage circuit of the instrument cluster for an open or for a short to ground. Refer to Testing for Intermittent and Poor Connections and to Connector Repairs in Wiring Systems.

Did you find and correct the condition?
Go to Step 12
Go to Step 9

8
Inspect for poor connections at the harness connector of the PCM. Refer to Testing for Intermittent and Poor Connections and to Connector Repairs in Wiring Systems.

Did you find and correct the condition?
Go to Step 12
Go to Step 11

9
Inspect for poor connections at the harness connector of the IPC. Refer to Testing for Intermittent and Poor Connections and to Connector Repairs in Wiring Systems.

Did you find and correct the condition?
Go to Step 12
Go to Step 10

10
Replace the instrument panel cluster. Refer to Instrument Panel Cluster (IPC) Replacement.

Did you complete the replacement?
Go to Step 12
--

11

Important
Program the replacement PCM.


Replace the PCM. Refer to Powertrain Control Module (PCM) Replacement in Engine Controls -3.5.L or to Powertrain Control Module (PCM) Replacement in Engine Controls 4.0L.

Did you complete the replacement?
Go to Step 12
--

12
Operate the system in order to verify the repair.

Use the scan tool in order to clear the DTC's that may have set in other modules during diagnosis.

Did you correct the condition?
System OK
Go to Step 2


Tachometer Inaccurate or Inoperative
Test Description
Step 4. This step tests the complete vehicle speed signal circuit from the PCM to the cluster, including the flat wire harness C215 to the IPC. For more information on flat wire circuits refer to Inline Harness Connector End Views in Wiring Systems.

Step
Action
Yes
No

Schematic Reference: Instrument Cluster Schematics

1
Did you perform the Instrument Cluster Diagnostic System Check?
Go to Step 2
Go to Diagnostic System Check -- Instrument Cluster

2
Install a scan tool.
Start the engine.
With a scan tool, observe the Engine Speed parameter in the PCM Engine Data 1 list.
Does the Engine Speed parameter match the tachometer display?
Go toTesting for Intermittent and Poor Connections in Wiring Systems
Go to Step 3

3
Turn the ignition OFF.
Disconnect the PCM connector C2.
Turn the ignition ON, with engine OFF.
Measure the voltage from the engine speed signal circuit to a good ground.
Does the voltage measure greater than 9.0 volts?
Go to Step 6
Go to Step 4

4
Test the engine speed signal circuit for an open, for a short to ground, or for a high resistance. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?
Go to Step 11
Go to Step 5

5
Test the ignition 1voltage circuit of the instrument cluster for an open or for a short to ground. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?
Go to Step 11
Go to Step 8

6
Test the engine speed signal circuit for a short to battery voltage. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?
Go to Step 11
Go to Step 7

7
Inspect for poor connections at the harness connector of the PCM. Refer to Testing for Intermittent and Poor Connections and to Connector Repairs in Wiring Systems.

Did you find and correct the condition?
Go to Step 11
Go to Step 10

8
Inspect for poor connections at the harness connector of the IPC. Refer to Testing for Intermittent and Poor Connections and to Connector Repairs in Wiring Systems.

Did you find and correct the condition?
Go to Step 11
Go to Step 9

9
Replace the instrument panel cluster. Refer to Instrument Panel Cluster (IPC) Replacement.

Did you complete the replacement?
Go to Step 11
--

10

Important
Program the replacement PCM.


Replace the PCM. Refer to Powertrain Control Module (PCM) Replacement in Engine Controls -3.5.L or to Powertrain Control Module (PCM) Replacement in Engine Controls 4.0L.

Did you complete the replacement?
Go to Step 11
--

11
Operate the system in order to verify the repair.

Did you correct the condition?
System OK
Go to Step 2

[wifesaurora]

I had the exact same issue, the tach would peg sometimes, ususlly on moderate to heavy throttle, then reset on a new ignition cycle. Was the Crank Position Sensor. Other symptoms (intermittant) stalling, slight almost imperceptable chug/surge when the engine gets to operating temp (usually only once per day unless it cooled for 6-8 hrs). If you have the original sensor (one on the 3.5, 2 on the 4.0) I would check them, if they haven't failed yet, they will.

[itsda5oh]

Mine is doing the exact opposite. Still to this day it will go to 0. Occasionally It will jump up higher then it should. In my case the connection(male/female) behind the tach becomes loose.

[blackaurora35]

Thanks for all your comments...all good info. I am betting on the Crankshaft positon sensor. Purchased one today, installing tomorrow. I did some research on installing it and it looks more complicated than I originally thought.

[blackaurora35]

An update: I changed the cranshaft position sensor last week and all is well so far. A few hints for anyone that thinks they want to tackle this job. It is definitely do-able but you will have to remove the starter. Very little room to get the starter out - disconnect the electrical connections - you may need to do this after removing the 2 starter bolts so you can maneauvor the starter around. I unbolted the engine mount and jacked the engine up a bit to get some extra clearance but it may not be necessary to do this.
I lost a lot of time trying to work starter out before I realized that the sensor electrical connection is on the same harness as the starter and not much play.
Thanks for all your help, I couldn't have done this job without you guys.

[brady]

2001 Oldsmobile Aurora 3.5 liter. This car is a great ride...becoming a classic!

Car will stall intermittingly at low idle or stopped. The RPM tach will sporadically shoot up to 8 when driving and engine seems fine. then goes back to normal. Occasional hard start.

Occasional jerk in gear shift. Everything I have researched puts all these symptons on a little crank shaft position sensor. Cheap part about $60 and is located under starter maybe 2 hours later.

Code came up for crank shaft position sensor.

Will change shortly.

These little buggers can cause all kids of annoying problems and are a common issue on this car as well as others.

Hope this does the trick! These cars handle great...smoother than caddies, have power, and almost as heavy as a Grand Marquis. Great gas mileage too. They are sporty and well designed and if you have one KEEP IT!

Also replacing the sensor will improve gas/mileage

One other interesting note the car was famous for breaking the frontal crash test machine(only one to do that) they had to start testing on a truck machine.

These are great mid size cars, and classy European front end way ahead of its time. Great lights, low beam, high beam and roads best lights ever.

[AuroraGirlFromMars]

The Instrument cluster was also ahead of its design by like 5+ years
also the sensor replacement wont improve gas mileage but if its bad it prob would. alsoooooooo crank relearn(im not sure if there is one on these but if so you need to do it)