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Jeep Grand Cherokee DTC 12, 24

Q. I am currently having problems with my 1997 Jeep Grand Cherokee. 4.0 liter 6 cylinder, 4WD, automatic transmission, fuel injection and ABS. The truck is not idling correctly. In park it idols too high and sometimes cuts off when I'm driving. I also don't think that the truck is going into overdrive. I recently washed the engine. The truck was running fine before then.

Jeep Grand Cherokee DTC 12, 24

After it was washed, the check engine light came on and I started having these problem. I tired to check the wiring connections to the plugs but couldn't find anything loose. The on board diagnostic indicated an error code #12 and #24. Could washing the engine have caused water to hinder the Throttle Position Sensor (TPS) operation? Could this be causing the car not to go into overdrive?

Another problem I have is with a noise in the differential. Ever since me wife purchased the car, there has been a roaring noise when we reach highway speeds. She spoke to a mechanic about it when she bought it, but he said that the roar was a common trait with that model and year vehicle. Any help on these items would be appreciated.

Thanks,
Shane

A. The DTC 24 indicates the TPS is either too high or too low. Obtaining the codes with a scan tool will narrow it down to exactly which it is. DTC 12 indicates battery input to the Powertrain Control Module (PCM) was disconnected during the last 50 key starts. So it would seem that you tried to clear the code by disconnecting the battery.

The TPS supplies the PCM and Transmission Control Module (TCM) with a signal for proper operation. If the signal is missing or bad, then it is very possible the transmission will not shift into Overdrive.

With the key ON, you should have about 4.5 volts at the orange (or white/black) wire at the TPS connector. If not, you have a problem with the PCM or the wire going from the PCM to the TPS.

If it's good then check voltage at the orange/dark blue wire. Voltage should go from 0 to 5.0 in a smooth and steady manner as you open the throttle. If it doesn't, you have a bad TPS. Then check the TPS ground at the brown/yellow wire and make sure the ground is good. If not, repair the ground wire as required.

I would recommend using an analog (needle type) voltmeter to do these tests. A digital meter is too slow to properly see the voltage rise.

Jeep Grand Cherokee DTC 12, 24

As for the noise in the differential, it is not unusual for them to make some noise, but without hearing the noise form your differential I can't tell you if it is excessive or not. Also, the noise may be coming from the tires. This is something to check before condemning the differential.

Axle gear noise can be caused by insufficient lubricant, incorrect backlash, tooth contact, or worn/damaged gears.

Gear noise usually happens at a specific speed range. The range is 30 to 40 mph, or above 50 mph. The noise can also occur during a specific type of driving condition. These conditions are acceleration, deceleration, coast, or constant load.

When road testing, accelerate the vehicle to the speed range where the noise is the greatest. Shift out-of-gear and coast through the peak-noise range. If the noise stops or changes greatly:

  • Check for insufficient lubricant.
  • Incorrect ring gear backlash.
  • Gear damage.

Differential side and pinion gears can be checked by turning the vehicle. They usually do not cause noise during straight-ahead driving when the gears are unloaded. The side gears are loaded during vehicle turns. A worn pinion gear mate shaft can also cause a snapping or a knocking noise.

Additional Information provided courtesy of ALLDATA

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