Broccoli: Corroded wiring causes TPS-voltage code - Transmission Digest

Broccoli: Corroded wiring causes TPS-voltage code

We had a 1999 Dodge 24-valve diesel truck that came into our shop with no fourth and no lockup. The truck had been at another shop, which had already replaced the accelerator-pedal-position sensor (APPS) and the powertrain control module (PCM) in an attempt to fix this complaint.

Broccoli: Corroded wiring causes TPS-voltage code

Shift Pointers

Subject: No fourth and no TCC lockup
Unit: 47RE
Vehicle Applications: 1999 Dodge Ram 24-valve diesel pickup
Essential Reading: Rebuilder, Diagnostician
Author: Denny Gipe

Shift Pointers

  • Subject: No fourth and no TCC lockup
  • Unit: 47RE
  • Vehicle Applications: 1999 Dodge Ram 24-valve diesel pickup
  • Essential Reading: Rebuilder, Diagnostician
  • Author: Denny Gipe

We had a 1999 Dodge 24-valve diesel truck that came into our shop with no fourth and no lockup. The truck had been at another shop, which had already replaced the accelerator-pedal-position sensor (APPS) and the powertrain control module (PCM) in an attempt to fix this complaint.

We immediately scanned the computer and found a P0123 code – throttle-position-sensor (TPS) voltage too high. When we looked at this PID in the scan tool, it reported a voltage range from 4.00 to 4.98 volts DC, yet using a multimeter on the signal wire from the APPS to the ECM we had a normal sweeping range of 0.5 to 4.5 volts. We could clear the code, but as soon as we started the vehicle it came right back. We then checked the TPS signal from the ECM to the PCM, and it too had a normal sweeping voltage while the scan tool indicated the 4.00- to 4.98-volt sweep.

We called ATSG and spoke with Wayne Colonna about this problem, and he told us how ATSG has seen a similar problem in Jeeps being caused by the horn’s clock spring in the steering wheel short-circuited to the cruise-control switch-sense circuit. I then suggested we try pulling fuses, and Wayne said it was a great idea, so we started pulling fuses one at a time. When we got to the horn fuse, we saw the TPS voltage in the scan tool drop to about 0.5 volts.

When we road-tested the vehicle with the fuse removed we had both overdrive (3-4 shift) and converter-clutch application. After returning from the road test we installed the fuse and, of course, the problem of high TPS voltage returned. We then pulled the relay for the horn, and that gave us the same results as pulling the fuse. So this isolated the problem to somewhere between the power-distribution center and the steering wheel. As we began tracing the horn wire from the relay we came across a large connector in the driver-side foot well to the left of the steering column (Figure 1). And there we found the wire looking green like broccoli, with the corrosion extending across other wires in this connector. So we unplugged it and cleaned everything up, and when we plugged it back in the problem was resolved.

I have been in the transmission business for 30 years and have 35 years of transmission experience. Although not having much electronic training – since it was not needed in the early days – I appreciate and use the services of ATSG. They have helped us solve some other weird wiring problems over the years. I have said for years now that as these computerized vehicles get older and older, corroding wires and connectors will be giving us some real headaches. This is a good example. Thank you, Wayne, and all the guys at ATSG.

Denny Gipe is the owner of Dennis Gipe Transmissions in Chambersburg, Pa.

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