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