P38A Gearbox

Hi all could someone please throw me a line in what could cause the p38 to throw gearbox overheat up when the car has only just been started after 12hrs. My thinking is low voltage but swmbo needed it for work so couldn't put meter on it. Will check that tomorrow. Is there anything else to check if that comes back ok.
Cheers all

poor sensor

Ok so checked alternator output and it's 13.97v after start up at the alternator and 13.67v at the battery. Does this mean the alternator is good or is on its way out and is the temp sensor the little blue thing on the side of the gearbox rad.

stemac33 said:

Ok so checked alternator output and it's 13.97v after start up at the alternator and 13.67v at the battery. Does this mean the alternator is good or is on its way out and is the temp sensor the little blue thing on the side of the gearbox rad.

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its working

Is the blue tab on the gearbox cooler rad the temp sensor if so anyone got a part no. All I can find is coolant temp sensors

stemac33 said:

Is the blue tab on the gearbox cooler rad the temp sensor if so anyone got a part no. All I can find is coolant temp sensors

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I take it this is an auto. If so. https://rimmerbros.com/Item--i-ESR4330

stemac33 said:

Ok so checked alternator output and it's 13.97v after start up at the alternator and 13.67v at the battery. Does this mean the alternator is good or is on its way out and is the temp sensor the little blue thing on the side of the gearbox rad.

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This a petrol? Diesel usually 13.8V. Petrol I would expect to be 14.2 - 14.5V.

Cheers wammers Yes it an auto 2.5td 1996. Got home teatime yesterday 5.30 ish and tried the beat started as usual and no gearbox fault. So put it down to a glitch or sensor. Wife went out at 9.30 to go to work and there she blows, gearbox overheat again with a stone cold engine and box. Is there anyway to test the sensor.

stemac33 said:

Cheers wammers Yes it an auto 2.5td 1996. Got home teatime yesterday 5.30 ish and tried the beat started as usual and no gearbox fault. So put it down to a glitch or sensor. Wife went out at 9.30 to go to work and there she blows, gearbox overheat again with a stone cold engine and box. Is there anyway to test the sensor.

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Sensor should be normally open circuit, warning when closed. Plug that connects it to loom is to N/S of radiator, you could check there is no frayed wiring causing a short to ground.

Will check teatime when I get home cheers

stemac33 said:

Cheers wammers Yes it an auto 2.5td 1996. Got home teatime yesterday 5.30 ish and tried the beat started as usual and no gearbox fault. So put it down to a glitch or sensor. Wife went out at 9.30 to go to work and there she blows, gearbox overheat again with a stone cold engine and box. Is there anyway to test the sensor.

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Unless you've changed the alternator or upgraded the set point I wouldn't expect more than 13.8V out of your alternator. Might be worth going through the electrical troubleshooting guide.

ok so have no resistance across the two pins from the sensor and 12v on one pin and nothing on the other from the loom so presuming that should be earth but if i test across them i have nothing, having tea now so will do more digging after.

stemac33 said:

ok so have no resistance across the two pins from the sensor and 12v on one pin and nothing on the other from the loom so presuming that should be earth but if i test across them i have nothing, having tea now so will do more digging after.

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No resistance across the sensor means there is a connection across the pins, i.e. it will throw a warning (see Wammers post #9). So sensor sounds shot. Unless it was hot.

Couldn't have been hot been stood since 8am. Would disconnecting the sensor cancel the warning

Just trawling through rave to find wiring diagram

So what I can gather from rave is ecu sends 12v to temp sensor and if sensor is detecting overheat it sends it to earth and the ecu picks up on this. Am I correct so far

stemac33 said:

So what I can gather from rave is ecu sends 12v to temp sensor and if sensor is detecting overheat it sends it to earth and the ecu picks up on this. Am I correct so far

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That's what Wammers said.

Does the earth go straight to earth or does it go through the ecu to earth. Can't seem to find that bit in rave.

stemac33 said:

Does the earth go straight to earth or does it go through the ecu to earth. Can't seem to find that bit in rave.

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Grounds at E154 L/H engine compartment. See Component location views Z5 Photo 26. Or for 1999 and on. E0557 Z5 photo 110.

Ok so retested plug from loom and have earth but also have 12v across the 2 pins with no keys in and ignition off. Thought this would be ignition live and not perminant live unless it is live when becm is awake?