Throttle Potentiometer - Fault Code Testing Procedure
CATEGORY: EngineSECTION: 2
PAGE: 27
ISSUE: 03/93-0311
CODE: 240
Subject:
Throttle Potentiometer Faults
(LH 2.4.2 with Electronic Throttle System)
Application:
1992 9000 Turbo
9000 models with Traction Control have a throttle potentiometer integrated into the throttle housing. This throttle potentiometer sends a signal to the Electronic Throttle System (ETS) control module. The ETS control module then creates a digital throttle position communication signal. This digital throttle position signal is sent from pin # 26 of the ETS control module to pin # 3 of the LH control module. The ETS control module changes the duration of the pulsed square wave as the throttle position changes.
Should a fault occur in the throttle potentiometer or ETS control module, Fault Code 25771 may be stored in the LH ECM. This bulletin covers the fault tracing procedure for LH Fault Code 25771 on ETS-equipped vehicles.
Cars Affected:
1992 9000 Turbo models
Action:
1. Check that there are no fault codes stored in the ETS system. Many ETS faults could cause an incorrect throttle position digital signal to be received at LH ECM pin # 3.
2. With all components connected, and the engine running, connect an oscilloscope or a Logic Probe (Figure 1) to LH ECM pin # 3.
^ With the throttle closed, you should find a square wave with a short "HI" logic level (green LED much brighter than the red one) and a long duration "LO" logic level. (See Figure 2.)
CAUTION:
BE SURE THE PARKING BRAKE IS SET, THE WHEELS ARE BLOCKED AND THE PATH IN FRONT OF THE VEHICLE IS CLEAR.
^ As you increase the throttle opening, you should see an increase in the duration of the "HI" logic signal (the red LED becomes brighter and the green one goes dimmer). The change will be much more dramatic if you place the engine under load. Stall test an automatic or let out the clutch in gear with the brakes on in a manual transmission car. (See Figure 3.)
3. If the logic level is a constant "HI", check for an open circuit between LH ECM pin # 3 and ETS ECM pin # 26. If the logic level is a constant "LO", check for a short to ground.