What do you mean by scoping? I know they have followed the wires from the coolant sensor to the ECM then to BECM and up to dash, and all the wires checked out good, including grounds. The wires to the dash are actually two power wires, and the ground must be in the harness somewhere. Kind of strange. Also we have checked for correct alternator/battery voltage, it was ok.

oscilloscope eg velleman hps140 pocket scope
 
Hi all, I am new here but not to the P38. I have had four of them.

Regardless, I have been looking all over the internet the last couple of days with no luck, have searched here as well as posted on RR.net.

I have an 02 P38 4.6 in the U.S. It has 66k miles on it.

Last week was driving along and it indicated overheating, which it has never done before. I immediately pulled over and popped the hood, it did not seem hot at all. When I got back in the car and gave it gas it went back down to the middle of the gauge.

I went to my local independent LR garage and they recommended I change the coolant temp sensor, which I had them do. After picking it up, I noticed that the gauge now does not move off of the blue line. It does move up to the blue mark, but not to the middle. When I put the ignition key in it also lights up the red overheat lamp in the gauge, which it is supposed to do.

Figuring maybe a faulty coolant sensor, they replaced with another brand new one. Still have the same result.

Was hoping it was perhaps a faulty gauage itself, but looking over various threads that seems unlikely. It does seem to point to the BECM?

Just angry because this is the SECOND becm I have had to change.

How should I proceed? I am mechanically proficient, but I can't use an electrical tester-volt meter- to save my life. The shop can't get back in for another 5 days or so.

Also, had a good look at this thread http://www.landyzone.co.uk/lz/f10/no-temp-gauge-198158-11.html
And he seemed to have the exact problems I am having, unfortunately that is on a diesel and I have a gas "petrol" engine

Where are you in US ? I'll be over in July and September and have MV Faultmate : you'll want your gauge problem fixed before that but you never know with the P38 !
 
Thanks for the offer...hopefully I'll have it fixed by then.

At the other poster...what is the reason for scoping the wires? If they have normal voltage/resistance/etc. what would we be looking for?
 
A scope will give voltage readings and also a graphical wave form-if there was interference-it would show.
 
A scope will give voltage readings and also a graphical wave form-if there was interference-it would show.

Would interference be a cause for gauge malfunction even though the wires to the cluster are receiving the proper voltage? What could cause interference?

An exhaustive Google search shows this is a very common problem, but no one ever updates their posts with the solution or fix if one was ever found!
 
Would interference be a cause for gauge malfunction even though the wires to the cluster are receiving the proper voltage? What could cause interference?

An exhaustive Google search shows this is a very common problem, but no one ever updates their posts with the solution or fix if one was ever found!
you can also check voltage with a scope at same time.

I haven't looked at a RR wiring diagram, but a scope can show data in a wave form- it is possible that if there is interference the wiring would work- but the gauge wouldn't.

I would also check and clean all the earths- if you have a bad earth it can cause all manner of weird faults


an odd question, does the gauge work at all correctly with hot engine ign on and engine not running
 
you can also check voltage with a scope at same time.

I haven't looked at a RR wiring diagram, but a scope can show data in a wave form- it is possible that if there is interference the wiring would work- but the gauge wouldn't.

I would also check and clean all the earths- if you have a bad earth it can cause all manner of weird faults


an odd question, does the gauge work at all correctly with hot engine ign on and engine not running

Interesting. All earths have been checked, please see the rest of this trhead. The only time the gauge works is when it is plugged into diagnostics. Otherwise, when ignition is on or truck is running, the needle will move a quarter inch off cold into the blue lines and remain there. The red overheat light turns on and off like it should upon startup.
 
Interesting. All earths have been checked, please see the rest of this trhead. The only time the gauge works is when it is plugged into diagnostics. Otherwise, when ignition is on or truck is running, the needle will move a quarter inch off cold into the blue lines and remain there. The red overheat light turns on and off like it should upon startup.
There was a diesel with exactly the same problem, turned out to be the sensor was the wrong one. With diagnostics, you can drive the gauge, so that's not the problem, look at the sensor readings with diagnostics, on the diesel, typically, it's a number between 0 & 255, not an actual temperature reading (will depend on whose diagnostics are used) 255 equates to 0C; 0 equates to fecking hot. If you can see the sensor reading and monitor it as the temperature of the engine rises, that will prove the sensor. If the sensor responds correctly and the gauge responds correctly that leaves the BECM. My guess is still the sensor.
 
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BeCM has been swapped as well as two coolant sensors. There is only one possible part number for the sensor, and it was right both times. As far as the readings, when I plug diag. In I can watch coolant temp rise and lower. It was showing anywhere from 87-97 degreesC. Or maybe that was just a value? Either way...
 
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Another bump...at a complete loss here. The shop is on very good terms and local to Atlantic British, a major LR parts provider for the entire U.S. They spoke and AB's tech team was just as stumped as everyone else. This is most frustrating by the fact that other people seem to have this problem but a solution is yet unknown! As it is, I wont drive the car because I don't know what the temp is, so it has been sitting for almost 2 weeks!:mad:
 
! As it is, I wont drive the car because I don't know what the temp is, so it has been sitting for almost 2 weeks!:mad:

But it'd take you 15 minutes to slap a simple remove Maplins (Radio Shack) temperature gauge (with setable alarm) on the car until you sort the problem - they cost under $20.
 
But it'd take you 15 minutes to slap a simple remove Maplins (Radio Shack) temperature gauge (with setable alarm) on the car until you sort the problem - they cost under $20.

No one has anything here local...would have be shipped. I will most likely be ordering one online and waiting a week or so for it to show up (which is why I normally refuse to shop online:rolleyes:)
 

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