1999 Td5 defender unresponsive temp guage.

Hi there.
Newbie to forum. Used it for info many times and thought it time to join. Hopefully I can pick a few brains with my problem!
Have got a 1999 td5 defender and have owned it since April or so. Problem is, when start engine from cold, temp guage goes to halfway and then drops off to zero after 5 mins of driving. Heater blows nice and hot, pulls very well no problems whatsoever except the guage not responding. Changed the sensor twice, (new one from eBay, didn't fix problem so new one from land rover). Changed guage, exact same. Disconnected plug from sensor, full deflection on guage. Dipped old and new sensors in warm water, both work as should, ie resistance goes up. Thermostat changed, coolant level correct, fan can be turned by hand ( with engine off!!) Did find oil at the red plug at ecu. Cleaned it out using correct spray etc. found orange plug seal sat next to ecu however. This has been put back as should be. Will be changing injector loom shortly. Two of my aircraft electrician mates did a continuity check from sensor to the ecu and this turned out to be fine. Few of us completely scratching our heads now.
Sorry for the mass of info but tried everything I can think of and more. Oh yeah, tested the ecu earth point to negative on the battery. Still no change. Have found that since fault finding, the guage starts at nearly fully hot ( just shy of the red) when engine is fully cold. Really don't know what to do. Please help!!

it's not enough to check just continuity...u must check the wiring for "isolated shortcircuit" to supply or earth too
1. both plugs must be "in the air" then give 12V through a 1A fuse directly from the battery on one pin at the sensor's plug and check with voltmeter at the ECU side between earth and both inputs and also on the other pin at the sensor... if the fuse blows or u will have a smaller voltage on one of the other wires it means the wiring is chaffed somewhere

2. check with ohmeter between each pin and earth...there must be fully open circuit(no reading at all)

3. the most relevant test is to get hold of a proper connector(to not cut the wires both sides)..and hardwire the sensor into the ECU's inputs(u must cut there the old wires....u can solder them back if everything's ok).

4. all the wiring measurements must be made on the wires from ECU to the gauge too

as you described everything and all the bits replaced there must be a wiring issue somewhere

you could rule out the wiring from sensor to ECU though by reading coolant temp. live data with a tester...if the live data looks good and the gauge stiil doesnt work the problem must be between the ECU and instrument pack (or in the worst case within one of them)

your gauge is working backwards! have you tested it with a computer/hawkeye yet? i have had some similar issues,ended up changing the complete harness system and then swoped computer boxes round between other vehicles untill i found a computer unit that worked correctly in both cars.(we have a fleet of 22 TD5 game viewing vehicles, so had the luxury of swoping units..) if you can figure out exactly what the issue is i would like to know as we solved the issue with dumb luck and never really got the right solution.

we swoped gauges,and sensors for new ones as well and still had the same issue until swopping computer units around...

My mate was looking at it today and he's sayin that from sensor to ecu is definitely fine. He did try and test from ecu to guage. From what I gather, the three plugs going into guage is earth, positive and the resistance measuring the temp. I'm not electrically minded but like you said, it appears the guage is working back to front. He wanted to cross connect wires on the guage to see what happens but was a bit scared In blowing something. am going to speak to local dealer and see if I can get a decent wiring diagram. The haynes manual seems to miss mine out! It goes from a 300tdi to a post 2001 td5. Does anyone know a site with a decent wiring diagram.
The guage does seem to flutter with a raise in revs. Could this just be from the alternator compensating for the increased revs. This could possibly point to a wire fault as opposed to a hardware fault with it showing on the guage. Maybe I am clutching at straws here? From what I have read, it is hard to find a compatable ecu for a 1999 td5 defender! If I do find the problem, will be sure to let you know what it is. Defo think that he next stage is hawk eye/diagnostic to see if the ecu is working as it should. Fingers crossed it is!!!

IMO the wiring diagram on that part from ECU to instrument pack is the same on '99 with '01 td5...if you didnt intrude in the ECU with remap or something and it worked normally untiil a point then it started to missbehave investigate well the wiring then read live data from ECU to make sure

I have only had the car for a few months and it was used as an estate/gamekeepers car so I don't think the ecu has been remapped or anything. In all the time I have owned it, the temp guage hasn't worked so I'm kinda starting blind. When I do get the ecu diagnostic test, would that show something up as say chaffing wires etc.? I was actually thinking of a remap later down the line as the engine only has 66k. Albeit I believe the ecu is a non flash type.

u must run circuit tests and read live data
1. read live data to see if the temp. sender's output reaches the ECU properly... read it with cold engine then with hot engine...with hot engine u must have around 90*C on coolant temp reading
2. u can activate the gauge through the tester to see if it gets proper inputs from the ECU

the tester will not tell you if the wiring is chaffed or not, it just gives inputs to the different components...the wires must be checked as i told you before.

if u have good live data in the ECU, and the gauge still doesnt show well if u are certain about the wiring from ECU to instrument pack then Rean could be spot on with the ECU missbehaviour

the wire change over wont work, the computer is way too clever for that, yes we tried everything....it sounds like somewhere down the line your vehicle got fitted with a discovery computer box, and that will be what happens, if you have a mate with a td5 ..buy him a bear and just ask to swop comps for a bit, if the gauge works correctly....well you have the answer, specially since it has never worked since you got it

there are only 2 ECU's compatible for Defender and Disco...others wont work at all...here are the part numbers in chronological order... the red ones are good for both ...eventually check the part number on yours to see which one it is:
(if your's a '99, normally it must have the MSB101170 unit)

DEFENDER


MSB101170 ELECTRIC CONTROL UNIT-FUEL CONTROL, 2.5L 5 CYL L/R TURBO DIESEL, TD5
MSB101171 ELECTRIC CONTROL UNIT-FUEL CONTROL, 2.5L 5 CYL L/R TURBO DIESEL, TD5
MSB101171 ELECTRIC CONTROL UNIT-FUEL CONTROL
MSB101360 ELECTRIC CONTROL UNIT-FUEL CONTROL, 2.5L 5 CYL L/R TURBO DIESEL, TD5
MSB000080 ELECTRIC CONTROL UNIT-FUEL CONTROL, 2.5L 5 CYL L/R TURBO DIESEL, TD5
NNN000120 ELECTRIC CONTROL UNIT-FUEL CONTROL, TD5
NNN500020 ELECTRIC CONTROL UNIT-FUEL CONTROL, BEFORE ORDERING PLEASE CHECK FOR SERVICE EXCHANGE VERSION, TD5
LR006328 ELECTRIC CONTROL UNIT-FUEL CONTROL, EXCHANGE PART (RE-MANUFACTURED), TD5



DISCOVERY

MSB101183 1 ELECTRONIC CONTROL UNIT ENGINE, MANUAL TRANSMISSION
MSB101184 1 ELECTRONIC CONTROL UNIT ENGINE, MANUAL TRANSMISSION
MSB101330 1 ELECTRONIC CONTROL UNIT ENGINE, MANUAL TRANSMISSION
NNN000120 1 ELECTRONIC CONTROL UNIT ENGINE, MANUAL TRANSMISSION
NNN500020 1 ELECTRONIC CONTROL UNIT ENGINE, COOLED EGR, CHECK FOR SERVICE EXCHANGE VERSION, MANUAL TRANSMISSION
LR006328 1 ELECTRONIC CONTROL UNIT ENGINE, EXCHANGE PART (RE-MANUFACTURED), COOLED EGR, MANUAL TRANSMISSION
NNN500250 1 ELECTRONIC CONTROL UNIT ENGINE, NON COOLED EGR, MANUAL TRANSMISSION
MSB101192 1 ELECTRONIC CONTROL UNIT ENGINE, AUTOMATIC TRANSMISSION, '(+)"EUROPE/J"'
MSB101193 1 ELECTRONIC CONTROL UNIT ENGINE, AUTOMATIC TRANSMISSION, '(+)"EUROPE/J"'
MSB101340 1 ELECTRONIC CONTROL UNIT ENGINE, AUTOMATIC TRANSMISSION, '(+)"EUROPE/J"'
NNN000130_USE 1 ELECTRONIC CONTROL UNIT ENGINE, AUTOMATIC TRANSMISSION, '(+)"EUROPE/J"'
NNN500030 1 ELECTRONIC CONTROL UNIT ENGINE, AUTOMATIC TRANSMISSION, '(+)"EUROPE/J"'
LR006301 1 ELECTRONIC CONTROL UNIT ENGINE, EXCHANGE PART (RE-MANUFACTURED), REAR, AUTOMATIC TRANSMISSION, '(+)"EUROPE/J"'
MSB101260 1 ELECTRONIC CONTROL UNIT ENGINE, (AUTOMATIC TRANSMISSION, '(-)"J"' OR AUTOMATIC TRANSMISSION, '(-)"EUROPE"')
MSB101261 1 ELECTRONIC CONTROL UNIT ENGINE, (AUTOMATIC TRANSMISSION, '(-)"J"' OR AUTOMATIC TRANSMISSION, '(-)"EUROPE"')
MSB101350 1 ELECTRONIC CONTROL UNIT ENGINE, (AUTOMATIC TRANSMISSION, '(-)"J"' OR AUTOMATIC TRANSMISSION, '(-)"EUROPE"')
MSB000130 1 ELECTRONIC CONTROL UNIT ENGINE, (AUTOMATIC TRANSMISSION, '(-)"J"' OR AUTOMATIC TRANSMISSION, '(-)"EUROPE"')

HI Guy's,
another Cornish newbiee, just reading this as I have the exact same fault on my 90 TD5 which I have recently bought......
This one has had a new loom fitted (as I requested this replaced B4 I purchased), new temp sensor, good chipped ECU (no oil), just fitted a new genuine gague this afternoon & guess what........... same fault :confused2:
from cold, gague half way, goes down when engine warms up & fluctuates when reved slightly........
Going to plug in diagnostics morrow AM when cold to see what temp sensor is sending/recieving & go from there..
Will let u know what I find if anything.........
Cheers, Ginger

Hi again,
Plugged into the defender this morning, engine temp @
3 degrees, gague just under red..?? Started n driven approx 8 miles with loaded
Trailer, gague on cold, ecu reading 78 degrees.....?!?!!!???
Am I goin mad or..........

Ginger c said:

Hi again,
Plugged into the defender this morning, engine temp @
3 degrees, gague just under red..?? Started n driven approx 8 miles with loaded
Trailer, gague on cold, ecu reading 78 degrees.....?!?!!!???
Am I goin mad or..........

Click to expand...

sounds like the actual temp sensor is showing the correct temp but the gauge isn't.

I know, but the gauge came out of an original land rover
Box yesterday.............!!!!

Anybody have success with this problem?