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JoeTampa71 06-06-2011 08:59 PM

Variable Speed Sensor?
I have a 2000 4.0L Laredo with QuadraDrive. My speedometer act erratically when my foot is not on the gas. I've looked around and found it is most likely the variable speed sensor. There's no check light or driving issues. I'm not sure what transmission I have 42RE, 45RE or 454RE. 2 questions:

  1. Would the sensor cause this?
  2. How do I tell what transmission I have?
Any help is greatly appreciated!

Thanks in advance,


StephenE 06-06-2011 09:21 PM

Re: Variable Speed Sensor?
If you have the 4.0l, then you have the 42RE transmission.
Speed Sensor:

JoeTampa71 06-07-2011 07:17 AM

Re: Variable Speed Sensor?
Thank you Stephen!

Frango100 06-07-2011 09:37 AM

Re: Variable Speed Sensor?
I would not expect the speedometer sensor on the transmission. The speed sensor on the transmission is used by the TCM for the shifting points. I know that the speedometer signal is coming from the PCM, but donīt know yet where the PCM gets this info from. Maybe from one of the wheel speed sensors. Will search further and let you know.

Frango100 06-07-2011 10:01 AM

Re: Variable Speed Sensor?
Some googling learned me that the PCM gets the speed info from the ABS control module. Its using the speed signal from the rear wheel sensors. Strange only that the problem is only there when decelerating (foot not on accelerator). Before changing any component, you could do the instrument cluster self check and see how the speedometer behaves, it should go to max scale and back to zero without any spikes. To go into the instrument self test mode, with ignition switch still in off, press the odometer reset knob and while holding it in, switch the ignition in on. You will see all indicators move to max scale and return to zero (also all lights will be tested and the odometer will test the display).
If this looks ok, you should go to some place where they have a scan tool which can access the ABS controller. There you can see any faults and also each wheel speed.

StephenE 06-07-2011 10:08 AM

Re: Variable Speed Sensor?
What he said... ^^^^^

JoeTampa71 06-07-2011 03:04 PM

Re: Variable Speed Sensor?
Thanks All. Good thing I didn't run out and get a VSS. It's only $18, but still. I will run the test this evening and post results.

JoeTampa71 06-07-2011 04:56 PM

Re: Variable Speed Sensor?
I did the test and only the speedo maxed out and returned to zero. After that it started acting erratic more often and sprung a check engine light.

Frango100 06-07-2011 05:48 PM

Re: Variable Speed Sensor?
Did you look for any fault code? If not, switch the ignition switch from off/on 3 times and let it in on, the odo meter will show you any fault code or "Done" when all ok.
But all the instruments should move during the test. Looks that your instrument cluster has a failure.

JoeTampa71 06-07-2011 06:34 PM

Re: Variable Speed Sensor?
I disconnected the neg battery terminal to reset the ECM and the check engine light did not come back on. I hope it's not the cluster cause it only has 86k and finding an 11 year old cluster with those miles will be difficult. I will try the ignition key 3X like suggested but not sure if a code will spring w/o a check engine light.

Once again, many thanks to all!

JoeTampa71 06-07-2011 07:22 PM

Re: Variable Speed Sensor?
It came up done but thanks for the info Frango! Jeeps came a long way since my CJs LOL.

Frango100 06-07-2011 09:36 PM

Re: Variable Speed Sensor?
During the instrument self test all instruments should go full scale and back to zero. If not, most probably the cluster has a fault. Donīt know if it can be a bad contact or maybe a bad solder. You could still try to go to a place where they can read the ABS controller faults, to see if its not an input fault.

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