Problem after fitting new engine mounts

[davebb]

Hi use the car ground and test one of the sensor wires for the full voltage,
the other wire will be the reading after the sensor,
and yes you should find your 5V,
Dave

[pierremcalpine]

Can you clarify - were you verifying values for the ECT (the bit that is embedded in the thermostat).

[TurboDiesel2006]

Thanks for that davebb.

I checked the coolant sensor temp readout after being left overnight and it reads -20.04 degC which is obviously wrong.

The moment I start the car it reads 89.96 degC, also wrong

But the resistance check across the terminals of the coolant temp sensor that I did yesterday was showing readings in line with what I would expect.

I checked the voltage from the coolant temp sensor cable to vehicle earth with the ignition switch at II and I am getting 0.0 VDC so something not right there.

I checked the voltage across pins 56 & 60 of the ECM and I'm getting 4.95 VDC which I believe is correct.

So I think I can conclude there is a problem in the loom between the ECM and the coolant temp sender connector.

I checked the resistance between pins 6 & 14 on the DLC and I'm getting 62 ohms which I think indicates the CAN is intact.

The loom is wrapped in a plastic mesh and looks to be very inaccessible. I have no ideas how to check it. Does anybody have any ideas?

[TurboDiesel2006]

I just did a continuity check between the pins 56 and 60 on the ECM connector to the coolant sensor connector and both checked out as good.

So I am getting 5 VDC across pins 56 & 60 on the ECM but not at the coolant sensor connector yet a continuity check on the cable says it is ok. I am confused.

[barrybritcher]

you will have corroded wires somewhere making high resistance - the car interprets the high value as a "cool" temp

[barrybritcher]

volts can often appear ok but current cant flow through the high resistance.

yes i've been watching too much diagnosedan on youtube

[cheshired5]

Originally Posted by TurboDiesel2006

I have checked the resistance across the terminals of the temp sender while using a laser thermometer on the housing and and they are pretty much bang on correct
23 deg C 2.0 kohm
30 deg C 1.5 kohm
39 deg C 1.0 kohm
50 deg C 0.75 kohm

With the engine running, does the resistance fall in a linear fashion?
i.e. Does resistance ever increase, even momentarily as the engine warms up?
You need to watch the meter like a hawk when testing manually like this and make use of the Min/Max facility if your meter has one in order to spot any anomaly.

[TurboDiesel2006]

I checked the resistance behaviour of the coolant sensor and it decreased in an orderly way in that I watched the multi-meter reading very carefully and it did not jump around. Using a laser thermometer on the sensor housing and recording the hottest spot I got the following:
30 deg C - 1.55 k ohms
40 deg C - 0.84 k ohms
50 deg C - 0.63 k ohms
60 deg C - 0.49 k ohms
65 deg C - 0.47 k ohms

I also checked the resistance between the 96 pin connector at the ECM and the coolant sensor connector as follows
Pin 56 - 0.3 ohms
Pin 60 - 0.4 ohms

I tried clearing the ECM-2000 code again without success (switch off engine, start & rev to over 1500 rpm, switch off, restart and let idle for approx 20 seconds).

I then noticed that the temp gauge in the dash was not registering. I tried to read the coolant temperature using Vida but it was constant at 89.96 deg C and clearly not being updated. I added a couple of other readings to see if it was a wider problem but they worked ok.

I then cleared the codes again and disconnected the battery for a few minutes. Then when I turned the ignition to II the temp gauge shot into the red and I got a red triangle and a High Engine Temp message although the temp was by now less than 60 deg C.

I also note that when starting just on the key with no throttle applied the engine immediately revs to about 1400 rpm and stutters a few times (a bit like a petrol engine when it is over-choked) before slowly slowing to just under 700 rpm which takes about 20 seconds. I think this is probably a by-product of the erroneous temp in the ECM but that is just a guess.

I am still completely baffled.

[cheshired5]

Test the voltage between the ECT plug contacts over an extended period with the engine running.
It should remain at 5V DC throughout so once again use the high/low/average function on the multimeter if available to record any anomalies.

[TurboDiesel2006]

Thank you for the advice. Will the engine run if No 1 multiway plug at the ECM is disconnected so I can measure the voltage across the pins 56 & 60 or can I remove the back of the plug? Previously I have measured it with ignition on only.