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940 & 960 940 coolant temp sensor "fault"

BradBrad @Brad Sunshine Coast, QLD

1991 940 with B230, LH Jetronic 2.4

The car regularly sets a fault code for the Coolant Temp Sensor. The fault can be reproduced almost every time I drive the car.

Scenario: I live on a mountain with a roughly 4km long climb. Most of the climb I have the throttle at 3/4 to wide open. The code will usually be set when nearing the top of the climb or just after getting to the top. It also occasionally sets the code when accelerating at other times such as moving away from a standstill at traffic lights which it was it did this morning. Ambient temperature has no influence on the problem. Whether it's hot or cold outside the fault will occur.

This has been ongoing for many months. I installed a new Bosch coolant temp sensor early this year but it hasn't fixed the problem. A few weeks ago I removed the inlet manifold to get to the plug. I sprayed contact cleaner into it, tried to tighten the female connectors by pressing down on them with a small screwdriver then applied some electrical grease. This stopped the problem for about 2 weeks but then it returned. Last week I unplugged the connector then plugged it back in again and wiggled it around a bit and the problem stopped for a couple of days but then returned.

I've just been resetting the fault at the diagnostic box in the engine bay when it occurs but that's become tedious and annoying now so I want to try to fix it.

Based on my previous attempts to fix this it seems to be a loose connector causing the problem. Is there any way to tighten them more effectively than by the screwdriver method that I've already tried? I'm also wondering if replacing the female pins in the plug might be the way to go. Is there possibly some other cause for this I may not have thought about?

Thanks for any input.

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Comments

  • You say you repaired the connector, which worked for two weeks

    Try connecting the wires directly, eliminating the plug as a test

  • Which coolant sensor are you having issues with, the one that sends to the gauge (stupid weird looking connector), the one that sends to the ecu (standard bosch ev1 connector) or the sensor in the coolant bottle?

    If its the first type, as ramrod said you can remove the connector housing and attach the pins directly onto the sensor.

    If its the second type, the bosch ev1 connectors are available from efi hardware and numerous other places for basically nothing, and they can be crimped with standard el cheapo crimpers.

    bgpzfm142
  • BradBrad @Brad Sunshine Coast, QLD

    This is the sensor for the fuel injection and ignition ECUs. The one that is a pain to reach under the inlet manifold. It's interesting (to me at least) that the fault code is only being set on the Fuel Injection side (code 123) but not on the ignition side.

    I saw the EV1 connector on efi hardware yesterday but they're out of stock. There are a couple of other places that have them though.

  • BradBrad @Brad Sunshine Coast, QLD

    Thanks Daniel

    I didn't come across these in my search earlier today. I'll pick one up and see how it goes.

  • Sweet hopefully that fixes it for you mate.

    I'd grab a bunch while you're there , half the connectors on the car use the same plug (knock, injectors etc)

    I've got a draw full of them as spares good to have around.

  • Most coolant temp sensors have a variable resistor in the sensor which has 2 wires that go back to the ECU it's connected to.

    LH2.4 uses a different style of sensor. It actually has 2 variable resistors which are both grounded to the sensor threads (engine block) and 1 pin goes the the fuel ecu and the other goes to the ignition ecu. If you mistakenly put the "conventional" sensor in it's place it will work but will give weird symptoms such as poor starting, high fuel consumption, low power or keep storing codes for the temp sensor. The fault codes are intermitant as it's not a completely faulty signal, it's just not what the ECU expects at certain times which is why the fault code won't trigger consistantly.

    Volvo list the LH2.4 temp sensor as being a black connector (Bosch) but aftermarket versions have changed and the colour is not indicitive of having the correct sensor anymore. The LH2.4 sensor is rare and most suppliers have/list the other, more conventional type.


    The odds are you have the incorrect sensor fitted which is why you're still getting the symptoms and fault codes.

    The Tridon TCS060 is a more easily availble alternative to the bosch part which in most cases would need to come from O/S

    timboBrad
  • BradBrad @Brad Sunshine Coast, QLD

    The coolant temp sensor I installed was from FCP Euro and was listed as the correct part for my car. It has a black connector.

    There are no performance problems and fuel consumption hasn't changed. It's only setting the code for the sensor on the fuel injection side.

    I'm planning to replace the female pins with new ones and see if that helps.

  • Have you tested the coolant temp sensor (and its wiring) voltage and resistance at the ECU?

  • I would check if you have continuity between either pin and the engine block when it's disconnected. If you don't, it's the wrong sensor for LH2.4. Many listings I've seen for this sensor are incorrect, it's a simple check and a common mistake to presume that you have the correct part, they look identical but function differently.

  • This info from the Volvo Pocket Data Book may be helpful.

    Below temp curve is from the Bosch data sheet, see also below.

    Below application list is from the Bosch data sheet - note the '032' is Curve A above.


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