Service manual

90-898303

4-19

Throttle Position Sensor (TPS)

The TPS transmits throttle angle information to the ECM which varies the

injector pulse width accordingly. Should the sensor fail, the warning horn will

sound. RPM will be reduced by the ECM. TPS settings are not adjustable.

TPS settings can be monitored with the Digital Diagnostic Terminal through

the ECM. Voltage change should be smooth from idle to wide open throttle. If

voltage change is erratic, TPS is defective.

a) Throttle Position Sensor (TPS)

b) Throttle Stop Screw

c) Roller

d) Pocket

THROTTLE POSITION SENSOR (TPS) TROUBLESHOOTING

If the throttle position sensor is out of the intended operating range when the

engine is started, the Electronic Control Module (ECM) will sense that the

Throttle Position Sensor (TPS) has failed. The warning horn will sound, check

engine light will illuminate, DDT will indicate failed TPS and the engine will go

into RPM reduction. When the engine is started, the throttle arm on the engine

must be against the throttle stop screw. Do not move throttle or fast idle

control lever forward.

• Check throttle cable adjustment. The throttle stop screw on the throttle

arm must be against the throttle stop on the cylinder block when the

engine is started. Pre-load the throttle cable barrel 1 or 2 turns if

necessary.

• Verify driver is not pushing on throttle (if foot throttle is used) or advancing

the throttle only on the control box.

• Check throttle cam to roller adjustment. If the roller is not down in the

pocket/valley area on the cam, there is a tendency for the roller to ride up

or down on the cam which causes the TPS link arm to push/pull on the

TPS lever resulting in changing values.

Notes

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