Throttle Position Sensor: Service and Repair

The throttle position sensor (TPS) is used on diesel powered engines only when equipped with an automatic transmission and/or an Exhaust Gas Recirculation (EGR) system. If the TPS is to be replaced on a diesel engine, it must be tested/adjusted after replacement.

REMOVAL
1. Disconnect electrical connector on bottom of TPS.
2. Remove two TPS mounting bolts.
3. Remove sensor from bracket.

INSTALLATION
1. Position TPS to mounting bracket. The electrical connector should be facing downward.

NOTE: The TPS is spring loaded. After positioning the TPS to its mounting bracket, rotate TPS on bracket in a counterclockwise direction until two bolt holes align.

2. Install and tighten two bolts.
3. Connect electrical connector on bottom of TPS.
4. Operate the throttle by hand to check for binding.
5. The TPS voltage must now be tested and (if necessary) adjusted. Refer to the following:






THROTTLE POSITION SENSOR TESTING & ADJUSTMENT

CAUTION: Before attempting to test TPS, verify linkage adjustment dimension. This dimension MUST be 126.5 mm (5.0 inches) BEFORE testing. For linkage adjustment procedures, refer to Throttle Linkage Adjustment-Diesel Engine.

CAUTION: Before testing TPS, verify that engine is set at correct low idle speed. Refer to Idle Speed Adjustment.

1. After confirming correct linkage adjustment and idle speed, proceed to the following:
2. Attach a paper clip into center terminal of TPS electrical connector. Do not remove connector from TPS for this test.
3. Attach positive lead of a voltmeter to this paper clip and negative lead to a good ground.
4. Turn ignition switch to ON position. Do not start engine.
5. The voltage at TPS center terminal should be 1.0 volt (+/- 0.2 volt) with linkage at idle position. At wide open throttle (WOT), output voltage must be 2.2-to-2.9 volts higher than at idle speed. If voltage is not correct, proceed to adjusting linkage.






6. The throttle lever rod connecting throttle lever to fuel injection pump lever is adjustable. To prevent damage to ends of linkage, attach locking-type pliers to flat located on throttle lever rod before loosening locknuts.
7. Loosen lever nut. This nut is close to the flat.
8. Unsnap lever socket from lever.
9. Slowly rotate the flat on linkage rod (lengthen or shorten) to achieve 1.0 volt (+/- 0.2 volts) on voltmeter with linkage in idle position. At wide open throttle (WOT), output voltage must be 2.2-to- 2.9 volts higher than at idle speed. DO NOT lengthen or shorten linkage rod more than 1 mm from dimension shown. If voltage requirements cannot be met by linkage adjustment (125.6 to 127.6 mm), replace TPS.
10. Tighten rod nut after adjustment.
11. With engine OFF, operate throttle from accelerator pedal and check for throttle lever action and binding. Be sure throttle lever stop is against low idle speed screw after throttle is released.
12. Be sure of wide open throttle (WOT) when accelerator pedal is pressed to the floor. This is checked by observing throttle lever breakover position. Proceed to the following:
a. Key OFF and engine OFF for this test.
b. Two people are needed for this test. From inside of vehicle, press accelerator pedal about half-way to floor. Movement of both throttle lever and throttle lever-to-injection pump lever linkage rod should be observed.
c. Continue to press accelerator pedal to floor. If throttle lever breakover is operating correctly, the throttle lever-to-injection pump lever linkage rod should have stopped moving while throttle lever continues to move towards rear of vehicle.
13. Again, check and verify low idle speed. Adjust if necessary