P38a ODOMETER PROBLEM

Is there anyone in this group that can tell me what is wrong with my odometer (mileage recorder)? I have a 1999 (T reg) 2.5 BMW Engine DSE Range Rover. The problem is that it is recording more miles than I'm actually doing. The trip recorder and the computer recorded miles are not effected by what is happening. Let me explain in an example.........I switch of the engine at the end of the day with the odometer reading 114232.7 miles, when I turn the key to switch on in the morning, the mileage will mysteriously jump to 114300.0. Always it will jump miles to the exact whole number. Sometimes it will jump to the next nearest ten miles (say 23.4 to 30.0) and sometimes to the next one hundred. The mileage display is digital, so it disappears when you switch off and can't tell when it happens. Are the three mileage recordings getting their figures from the same (I presume) PCB board? Could it be a power surge when I turn the key? I hope someone can give me some idea or clue as to what is going on. My 4x4 service specialist has no idea except changing the board or dash and says it could be expensive.

Thanks in advance

Steve

spm> the morning, the mileage will mysteriously jump to 114300.0. spm> Always it will jump miles to the exact whole spm> number. Sometimes it will jump to the next nearest ten miles spm> (say 23.4 to 30.0) and sometimes to the next one hundred. The

Wierd. I can't tell you for sure, but...

The mileage is stored in two places on the vehicle: the BeCM and the instrument binnacle. At each engine start, the two compare notes ("I've got 114324.3" "I've got 76543.1") and then both store the HIGHEST value.

Your BeCM is obviously dropping bits somewhere and artificially increasing the values.

The BeCM certainly only reports to the nearest 100 miles diagnostically, but I don't know how much more detail it stores internally.

The figure itself is derived from the ABS sensors - the average of all

4 wheels is converted into a frequency-modulated signal of 8,000 pulses per mile, which goes from the ABS ECU to the BeCM, and then to other ECUs which depend on this information. I don't know, from memory, how this gets to the odo. display.

Now, there's a couple of things that could be happening

1) Something is causing the voltage on the ABS output to fluctuate which the BeCM is seeing as pulses as incrementing the counter overnight. If this were the case, I'd expect other symptoms like excessive battery drain because the computer is being kept awake.

2) The BeCM is faulty and the number being stored is getting corrupted.

3) There's a dodgy wire or connector on the link between the two which is causing the communication between them to get garbled.

Not a conclusive answer, but at least a plausible explanation. I can look up some specifics on the wiring diagram if you want - drop me an e-mail if you do, as I might miss a reply here (replace "spam" with "andy" to reply).

Andy