Dispatch 1.9 DCN2 Coolant Sensor Fault, Flashing Stop & Fans running constantly.

[pete12345]

Hi all, My brother's 2004 Dispatch has developed a fault with fans running constantly, temp gauge showing max with temp warning light & flashing Stop in the centre of the cluster.

We did diagnostics on the ECM (1.9L WJY LUCAS DCN2) & found "P0117 Coolant Temperature Signal Short Circuit To + Or Open Circuit"

• Sensor replaced with new one - no change

• checked new & old sensor resistance from cold to hot & both are 6-8Kohm cold down to few hundred ohms in kettle.

• Checked wiring to ECU - no shorts or breaks in the sensor wires

• Voltage at sensor = about 2V. (sounds wrong)

• Cleaned all connectors with contact cleaner

• Tried with sensor either open or shorted & no effect on temp gauge.

After allowing engine to cool, diagnostics said 20degC. Ran the engine, and the diagnostic temp went up to 100degC in about 3-5mins. Checked engine with IR Thermometer, and max we could find is about 60degC. Radiator top hose = 45degC. Conclusion: thermostat must be opening, but max fan speed is keeping the engine cool.

My understanding is the sensor should have 5V on one side ? Is the 5V regulator inside the DCN2 ECU, or elsewhere ?

Any ideas what to check next ?

Thanks,
Pete

[GiveMeABreak]

Have you checked / replaced the relay for the fan motor operation? Should be a 25 Amp Violet or Green Relay.

[pete12345]

Not yet. But how would a fan relay cause the P0117 coolant sensor fault ?

[GiveMeABreak]

Do you have the VIN handy so I can see what exact system you have? Please post your VIN in full without spaces - it will be automatically masked from public view after submitting your post & will only be visible to staff.

[pete12345]

VIN on the V5C is VF7**************[VIN obfuscated, can be read by forum staff]

Dispatch 815 Enterprise
1898cc
Registered July 2004

[GiveMeABreak]

Ok, so very little I have on this engine given the age now, but for the thermostat:

Temperature

Start of opening	83 deg. C
End of opening	95 deg. C

Here's a Diagram of the Cooling system in case that helps:



With the exception of the wiring codes, most of the component codes are indexed here:

PSA Electrical Diagrams - Wiring & Symbols Codes Index

[pete12345]

ok thanks, that's useful. We have not found item 4020 - Coolant Switch yet ?? Only the single sensor on the thermostat housing. Is there another one somewhere hidden ?

The thing I find wierd is the ECU sees the temperature rise from 20deg to 100deg, but still reports the sensor open or short circuit ??

[GiveMeABreak]

This is the sensor on a 2002 C3 - it's not the same housing as yours, but similar and shows the temp. sensor from the outlet tank:

viewtopic.php?p=547551#p547551

All I can suggest is that make sure you use a quality part - cheap sensors are known to be dead on arrival, so get a branded one if you don't already have one.

[pete12345]

ok. Do you know the resistance specs for the correct sensor ? The fault persists regardless of the sensor being connected or not.

Also any suggestions on why we only see 2V instead of 5V to the sensor from the ECU ?

[GiveMeABreak]

They don't show that info.

[PaulC5]

You could connect the old sensor to the wiring but not installed in the housing and see what temperature it suggests, then put in hot water and check again. This might help if checking the wiring. If you buy another sensor do the same before installing.

[pete12345]

You could connect the old sensor to the wiring but not installed in the housing and see what temperature it suggests, then put in hot water and check again. This might help if checking the wiring. If you buy another sensor do the same before installing.

Already tried that, but fault persisted with either sensor, and both open & short circuit.

Wierdly this morning my brother reported that several times it went back to normal with the gauge at 65deg & no flashing warning. My guess we have an intermittent connection in either the sensor or ECU connectors, or possibly a ground wire somewhere.