Odometer fault

seanmull · Apr 26, 2023

1997 p38 dse, proper mileage 150000 miles. It has started showing odometer fault and mileage reading around 100 miles instead of 150000 . Happening very often this week . Any help appreciated. Thank you

kermit_rr · Apr 26, 2023

That's a new one, any other issues? Does it run ok?

seanmull · Apr 26, 2023

kermit_rr said:
That's a new one, any other issues? Does it run ok?

Running perfect . It is the only fault

romanrob · Apr 26, 2023

Might be damp got to it somehow?

Datatek · Apr 27, 2023

seanmull said:
1997 p38 dse, proper mileage 150000 miles. It has started showing odometer fault and mileage reading around 100 miles instead of 150000 . Happening very often this week . Any help appreciated. Thank you

Is the mileage exactly 150000? It's odd that it shows 100. I'd pull out the cluster and look for dry solder joints and corroded connectors. Is the underlay in the drivers footwell wet by any chance?

seanmull · Apr 27, 2023

Datatek said:
Is the mileage exactly 150000? It's odd that it shows 100. I'd pull out the cluster and look for dry solder joints and corroded connectors. Is the underlay in the drivers footwell wet by any chance?

Most of the time it is 100 miles but I have seen 128 and 96 . Out of 6 starts today it was wrong twice . I will check the footwell for dampness this weekend

Grrrrrr · Apr 28, 2023

Blimey, I thought he was dead!

Odd, especially as it usually takes the highest reading of the cluster / BECM. To fail both you'd have to assume it is the part doing the comparison or the display itself.

Datatek · Apr 28, 2023

Grrrrrr said:
Blimey, I thought he was dead!

Odd, especially as it usually takes the highest reading of the cluster / BECM. To fail both you'd have to assume it is the part doing the comparison or the display itself.

The cluster mileage is updated by the BECM, the only time the highest reading comes into play is if there is a significant difference, the comparison is done in the BECM.

seanmull · May 1, 2023

All good with past three days , no fault at all. Hopefully I won’t see it again

seanmull · May 7, 2023

fault is back this fault is coming up on Hawkeye . Would it be the cause of my fault ?

lynall · May 7, 2023

I have seen the same on boat digi hour meters, stick gauge in the airing cupboard for a few days and off they go again.

Datatek · May 7, 2023

seanmull said:
fault is back this fault is coming up on Hawkeye . Would it be the cause of my fault ?

The ABS sensors are used for speed on the P38, so check the sensor outputs. I think only one is used for speed but I can never remember which one.
I suspect it will turn out to be a connector problem or damp around the BECM.

Grrrrrr · May 8, 2023

Datatek said:
The ABS sensors are used for speed on the P38, so check the sensor outputs. I think only one is used for speed but I can never remember which one.
I suspect it will turn out to be a connector problem or damp around the BECM.

I thought it averaged the 4? Maybe the WABCO C and D are different?

Datatek · May 8, 2023

Grrrrrr said:
I thought it averaged the 4? Maybe the WABCO C and D are different?

You may be right, I can't remember, I would have to delve into the detail to find out and I don't have the time. However one malfunctioning would still affect the a average would it not?

Grrrrrr · May 8, 2023

Datatek said:
You may be right, I can't remember, I would have to delve into the detail to find out and I don't have the time. However one malfunctioning would still affect the a average would it not?

I don't know. Would it count it as zero and pull the average down or NULL and just ignore it apart from throwing a fault code? I'm on my phone otherwise I would have a look at RAVE.

pwood999 · May 8, 2023

My RAVE doesn't say if it's average or not. Simple check would be to disconnect one sensor & see what the ECU says about speed.

Mark Piercy · May 8, 2023

I'd of thought if the fault was at the wheel end there would be an abs fault logged, maybe it's between the abs ecu output and instrument cluster? The abs ecus can get corrosion problems from leaking pollen filters or pollen filter casing seals to the bulk head.

Datatek · May 8, 2023

Mark Piercy said:
I'd of thought if the fault was at the wheel end there would be an abs fault logged, maybe it's between the abs ecu output and instrument cluster? The abs ecus can get corrosion problems from leaking pollen filters or pollen filter casing seals to the bulk head.

The ABS output goes to the BECM. I think the fault lies either in the instrument cluster or between the cluster and the BECM. As far as I can work out, the BECM receives the pulses from the ABS ECU and converts them for the milometer to something that can be saved in memory. Every time the BECM mileage memory is incremented, the BECM does a read and compare of the instrument cluster memory. Normally, having just been incremented, the BECM number will be greater than the instrument cluster number, so the new number is written to the instrument cluster. If the instrument cluster memory contains a number greater than the BECM, the instrument cluster memory will not be updated, instead the instrument cluster number will be written to the BECM.

Grrrrrr · May 9, 2023

pwood999 said:
My RAVE doesn't say if it's average or not. Simple check would be to disconnect one sensor & see what the ECU says about speed.

View attachment 287848

Thinking about it, it must take an average otherwise there would be a difference in the mileage between LHD and RHD countries bexause of all the roundabouts.

Datatek · May 9, 2023

Grrrrrr said:
Thinking about it, it must take an average otherwise there would be a difference in the mileage between LHD and RHD countries bexause of all the roundabouts.

That would certainly make sense.

Odometer fault

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