1997 Ford Ranger low voltage to coolant sencer

  • 1997 FORD RANGER
  • 4 CYL
  • 2WD
  • 72,000 MILES
Ive replaced the coolant sencers in this truck and keep getting low voltage to coolant sencers (replaced sencers 3 times to rule out the sencer) not sure where else to look for futher problems
Do you
have the same problem?
Saturday, March 21st, 2009 AT 12:36 PM

1 Reply

Not sure what you mean by low voltage, but the coolant sensor (among many others) work at a voltage level of about 5 volts. There should be a grey/red-stripe wire going to the following sensors; they all share the same common 5-volt reference voltage according to the wiring diagram I looked at:

Coolant Temp Sensor
Throttle Position Sensor
Power Steering Pressure Switch
Pwr Steering Jumper Switch
Octane Adjust Shorting Bar (Near PCM)
Intake Air Temp Sensor
Transmission Fluid Temp Sensor
Camshaft Position Sensor (Behind Oil Pump)
Turbine Shaft Speed Sensor
. Most importantly. Pin #31 of PCM
O2 Sensor B1S1 (even though the wire is orange)
O2 Sensor B1S2 (even though the wire is orange)

As stated, voltage should be around 5V for each of the components listed, at the Grey/Red-stripe wire measured to ground.

Voltage specifically for the Coolant sensor should be
50 Degrees F: 3.51 volts
212 Degrees F: .46 volts
230 Degrees F: .35 volts

As temperature increases, the resistance to the temp sensor decreases, causing the voltage to drop across the sensor 2 wires. So, you'll be taking measurements with a digital voltmeter across the sensor, not from either wire to ground. If you go from the sensor to ground, you'll actually see a voltage increase from the signal wire.
The only time you'll be using your voltmeter to ground is to verify the 5 Volt available at the Grey/Red-stripe reference voltage wire.

Finally, if you do have "low voltage" at the coolant sensor, the PCM should be setting a code P0117: Engine Coolant Temp Circuit Low.

Good luck.
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Wednesday, March 25th, 2009 AT 8:33 PM

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