F-150 Speedometer Woes
Recently I got involved in a call on a 2001 F-150 with a complaint of no speedometer. There was also a code P0500 (vehicle speed sensor) in the powertrain control module (PCM) and a code U1262 in the hybrid electronic cluster (HEC). On this vehicle, the HEC receives the vehicle speed input from the PCM over the standard corporate protocol (SCP) communication network.
Part of the challenge on these vehicles is the lack of information specifying where the PCM gets the vehicle speed input from. Normally the vehicle speed input is determined by the output shaft speed (OSS) sensor on all vehicles, except mechanical shift on the fly (MSOF) four-wheel drive (4WD) vehicles. On these vehicles, the PCM uses a transfer case speed (TCS) sensor.
When I started talking to the technician, we discussed the fact that a valid OSS reading was showing on his scanner, which should have been all that was needed, as this was an electronic shift on the fly (ESOF) 4WD vehicle. He verified there was no wire at the PCM connector that could go to the TCS sensor. Every time the vehicle was driven, code P0500 would consistently reset and the speedometer was always inoperative.
We discussed possible SCP network issues due to the code U1262, which indicates an SCP network communication problem, though there were a couple indications that the HEC and PCM were communicating. First, the passive anti-theft module is part of the HEC on this vehicle. The vehicle started and ran, meaning the HEC was providing the PCM the ignition key ID. The odometer, which is digital, was showing mileage, but just would not increase while driving. Normally on this system, if the HEC does not receive data from the PCM, the odometer will simply show dashes.
At this point, my suggestion was to try doing a fresh/blank programming on the PCM. We have mixed results doing this as the integrated diagnostic system (IDS) software keeps changing and it’s getting harder and harder to work around it. I suggested leaving the PCM disconnected and starting a new session with the IDS. This would allow us to start with a clean slate and not have the IDS pull any information from the PCM during the vehicle ID. Once the new session was started, a standard programmable module installation (PMI) was done. The PMI function is used when installing new modules in a vehicle. If the scanner is not able to retrieve the information from the old module it will normally either prompt the technician to enter what Ford calls “module build data or as built data” or it will go to the Internet and retrieve the necessary vehicle information. When prompted to install the “new” PCM, the tech did so, clicked OK, and the IDS programmed as we hoped it would. The best part was that once the PCM was programmed, the P0500 code was gone and the speedometer worked!
This is another classic example of how (even when everything is done correctly) technology is not always on our side. And why our Carline Specialists will normally recommend trying to install a module using the “as built data”– so the chance of getting bad information programmed into the new module is minimized.
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