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Discussion Starter #1
Group,

Bosch/Thor having what I believe is a bad cluster temperature circuit, I currently use a Bluetooth dongle app for my temp reading. The temp sensor is reading fine (replaced already). I have checked the grounds and my data PID is good via OBD2. Feeling the gauge in the cluster was at fault, I replaced the gauge out of donor cluster. No improvement. Next step would be to replace cluster and deal with the odometer error.

Beforegoing there, and having a few donor clusters I wanted to ask if anyone knows what portion board of the cluster (boards) can be utilized to replace the temp gauge circuit, or if the Odometer security is Siamesed into those used. The cluster is simple to break down after replacing the temp gauge initially. I could fix the lack of a functioning gage and avoid the Odometer issues of swapping the entire cluster. Has anyone made a Franken cluster in order to accomplish a similar fix? I have been unable to find a cluster diagram. Thanks in Advance. Joe
 

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Going in entirely the wrong direction. Do not change clusters for this issue The sensors always read fine. The sensor should be used to install an aftermarket gauge if you are concerned about overheating. The signal from the very accurate sensor is heavily buffered before it reaches the cluster gauge. The gauge is only as accurate as the signal it receives. The gauge hits centre when the engine is up to temp and the thermostat is open. It will not budge until you are already well past operating temp. At this point it climbs very quickly to red because... it's too dang hot already. You will never have an accurate factory gauge no matter what you change. If it were accurate it would fluctuate so much that every nonmechanical person drive a P38 would be in a full state of panic. get a spade splitter to keep the original signal line live as a back up... or novelty. Use the splitter to install a real gauge in the cabin. If you don't have NAV you can mount it in the cubby, folks have mounted them where the clock is or gone digital where the ashtray is.
 

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I appreciate the input and The Bluetooth OBD2 gives me what I need in accuracy, but I am not have working what I want to work and this is more of an exercise in understanding the circuit and finding the cause of the inoperability of the gauge. I am close and just would like it o work,even if it is for the next owner, my spouse kids that should have the cluster functioning as intended as filtered as it may be.
 

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LEGACY VENDOR
1995-2002 Range Rover P38A
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If you have a cluster with a lower mileage, then you can fit that, and you'll get the odometer error come up - but it is possible to then resync the BECM/cluster to the higher mileage (in this case the BECM... if the cluster has a higher mileage, it will overwrite the BECM mileage without warning.

It is possible to swap the mileage chip from one board to another, but it's a fair bit of soldering work, as each chip has 20+ legs to be freed before the chip will come out. I have done it before (for other reasons, not a faulty gauge) and then put a ZIF chip socket on the board, so that the chip then just presses in.

I'm not going to post on an open forum about which chips etc you need to meddle with, but if you drop me a PM I will give you some pointers.

Marty
 

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Why not replace the sender? The Thor uses a sender that is two in one, one to drive the engine ECU and hence the OBD signal and a totally separate one that supplies the signal for the gauge. If you've swapped clusters and it made no difference then it's likely the sender.
 

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Well that is part of the issue. We have no clue what year or model he has because he hasn;t posted nor is it in his signature.
 

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He says in the original post that it's a Bosch/Thor, model is irrelevant (as long as it is a P38). If the green wire at the 4 way connector on the sender is grounded and the gauge reads hot (gauge is heavily damped so will take a few seconds to climb), then it is the sender at fault.
 

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Actually it is relevant. There are different sensor part numbers depending on SAI for Bosch with entirely different locations
 

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I have too much experience with a faulty temp gauge (thor) for my liking. I too replaced temp sensor (on engine, the one on the radiator is for fuel mixture), had my BECM checked and replaced the gauge cluster to no avail. There are 4 wires on the temp sensor - 2 go to the ECU, 2 go to the BECM (green and black). The one's for the BECM are the ones for the gauge. From the BECM the fuel level and temp gauge are sent thru a serial link. So if your fuel gauge is working I don't see how that can be the culprit. I'd first try re-grounding the black wire from the sensor. The try rerouting the green wire all together from the sensor to the BECM (I can't recall if it's pin number 19 or 20 on the large green connector on the front of the BECM. The last method is something I am trying when I have the time in the next several weeks.
 
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