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P0117. "Low Engine coolant Temp Sensor Circuit."

Help, Advice and DIY Tutorials on Volvo's extremely popular car line -- Volvo's 1990s "bread and butter" cars -- powered by the ubiquitous and durable Volvo inline 5-cylinder engine.

1992 - 1997 850, 850 R, 850 T5-R, 850 T5, 850 GLT
1997 - 2000 S70, S70 AWD
1997 - 2000 V70, V70 AWD
1997 - 2000 V70-XC
1997 - 2004 C70

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shihabafi
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P0117. "Low Engine coolant Temp Sensor Circuit."

Post by shihabafi »

So, I've got my 850 that's throwing a P0117, and as with everything else, it's ripping me apart on the inside. The car hesitates for a few seconds when I try to start it, and the fan runs from the moment I put the key in, until a good 5 minutes after the car is off.

We got a "new" sensor from the junkyard, but I think it's also bad. I'm getting 5v from the wire going into the sensor with the car on II
IMG_20180831_081744.jpg
IMG_20180831_081740.jpg
Any ideas?
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misha
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Re: P0117. "Low Engine coolant Temp Sensor Circuit."

Post by misha »

You shoud check for resistance not volts.
Resistance is temperature dependant and at operating temperature should be around 300ohms.
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RickHaleParker
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Re: P0117. "Low Engine coolant Temp Sensor Circuit."

Post by RickHaleParker »

5V is the feed voltage, the voltage is supplied by the Engine Control Module (ECM). The same voltage source supplies the throttle position sensor. If you want to do this by voltage, you should be looking at the voltage drop across the sensor.

Leave the sensor disconnected, see if the symptoms change.
Pick a resistance from the table, place the resistance across the harness (disconnected from the sensor), see if the symptoms change.

Test the sensor:
1. Stick it in a glass of ice drip water, the resistance should be ~7300Ω
2. Bring sensor up to room temperature 68°F, the resistance should be ~2800Ω
3. With the engine at operating temperature, the resistance should be ~300Ω
4. Stick the sensor in boiling water,the resistance should be ~150Ω

Or you could put a the sensor in a pan of ice cold water then monitor the water temperature and resistance as you heat the water.

Engine coolant temperature sensor resistance table.
32°F (0°C) .............................................. 7300Ω
68°F (20°C) ............................................. 2800Ω
176°F (80°C) ............................................. 300Ω
212°F (100°C) ............................................ 150Ω

Possible sources for EFI-123 (P0117)
  • Signal too high:
    short-circuit to supply voltage in signal cable
    open-circuit in signal cable or ground lead
    contact resistance in terminals
    defective engine coolant temperature (ECT) sensor.
Signal too low:
  • short-circuit to ground in signal cable
    defective engine coolant temperature (ECT) sensor.
Faulty signal:
  • defective engine coolant temperature (ECT) sensor
    defective coolant thermostat
    contact resistance in terminals
    short-circuit between signal cable and another cable.
1998 C70, B5234T3, 16T, AW50-42, Bosch Motronic 4.4, Special Edition package.
2003 S40, B4204T3, 14T twin scroll AW55-50/51SN, Siemens EMS 2000.
2004 S60R, B8444S TF80 AWD.
2005 XC90 T6 Executive, B6294T, 4T65 AWD, Bosch Motronic 7.0.
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Re: P0117. "Low Engine coolant Temp Sensor Circuit."

Post by mrbrian200 »

Careful Rick,
Voltage drop across the sensor: you would need to know the internal resistance of the ECU between the signal input to ground to be able to calculate what the voltage drop across the sensor should be at a given temperature to make a meaningful assessment. If there are any diodes/transistors in the internal ECU circuit path (likely) it might get, well, complicated. Without an internal schematic for the ECU, or a table of voltage drops at various temperatures from a known good sensor its a moot issue.

Probing the isolated/disconnected sensor with an ohmmeter at various temperatures is the way to do it. That table of values is known, as you listed them.
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Re: P0117. "Low Engine coolant Temp Sensor Circuit."

Post by RickHaleParker »

The statement is carefully worded. Read what is there and nothing more.

One could calculate the internal resistance of the ECU, using 1. measured sensor resistance 2. voltage drop across the sensor 3. the feed voltage. From them three measurements, the remaining resistance in the loop can be calculated.

Measuring the voltage drop across the sensor without knowing the internal resistance of the ECU is not necessarily useless.
Assuming shorts or opens in the harness have been eliminated ...
If the voltage drop across the sensor = the feed voltage, the sensor is open.
If the voltage drop across the sensor = Zero, the sensor is shorted.
If the voltage drop across the sensor does not change with temperature, the sensor is completely dysfunctional.
1998 C70, B5234T3, 16T, AW50-42, Bosch Motronic 4.4, Special Edition package.
2003 S40, B4204T3, 14T twin scroll AW55-50/51SN, Siemens EMS 2000.
2004 S60R, B8444S TF80 AWD.
2005 XC90 T6 Executive, B6294T, 4T65 AWD, Bosch Motronic 7.0.
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