Explorer: Testing the TPS (throttle position sensor). ECM code 124

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By Mark Strickland

These instructions are for a 1992 Ford Explorer

with the 4.0L MFI engine.  Other years of this generation should be


Code 124 is stored in the

Electronic Control Module (ECM) continuous memory when the TPS signial

is higher than it should be as compared to the MAP/MAF/BARO/ACT sensor


If Code 124 is stored along with other

(TPS) related codes you should work on the lowest number of these related

codes before continuing with code 124 diagnostics

Step 1 Connect the (+) lead of a DIGITAL voltmeter to the Grey/White

wire at the TPS harness connector.  Connect the (-) lead to the Grey/Red

wire at the same connector

Step 2 With the Key on (ENGINE OFF) and the throttle closed the

voltage should be .71-1.29 volts.  Slowly open the throttle. 

As the throttle is opened the voltage reading should EVENLY increase to 

4.25-4.89 volts at wide open throttle.  If any uneven change occured

in the reading as the throttle was opened or the minimum or maximum voltage

ranges were not in line the TPS is most likely BAD.

If no fault is found in the TPS test

then test the Air Charge Temperature (ACT) sensor output.  A bad ACT

sensor can cause a lean or rich condition and have an adverse effect on

ignition timing.

Step 3 Connect the (+) lead of a DIGITAL voltmeter to the Light

Green/Purple wire at the ACT sensor harness connector.  Connect the

(_) lead of the voltmeter to the Grey/Red wire at the ACT sensor harness

connector.  With the key on (ENGINE OFF) the initial reading should

be 2.5-3.2 volts when the motor is at room temperature (75 degree F.)

Step 4 Start the engine and let it warm to operating temperature. 

As the engine is warming the voltage should evenly decrease to 1.5-.25

volts at operating Temp.

If no fault was found with the ACT sensor

then the ACT and TPS are working correctly.  Either the problemis

too intermittent to locate at the present time or another sensor is not

working correctly.  If the vehicle will not idle when cold or seems

to idle low even when warm you may have a bad AIC solenoid (Air idle control). 

This device changes idle by allowing more/less air to bypass the throttle.

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