Workshop Hints

Workshop Hints

Air Management
Unmetered air leaks can be misleading when diagnosing faults causing Malfunction Indicator Light/driveability complaints.

Crankcase Ventilation System
A fault in this system can often mislead diagnosis. This type of fault can produce:


^ Mixture/misfire detected codes
^ Whistling noise
^ Performance/driveability complaints

Throttle Position Sensors Testing





The Throttle Position Sensors can be tested with the following methods:
^ DISplus Status Page (approximately 0.5v. to 4.5v)
^ DISplus Oscilloscope Select from the Present measurement which requires taking the measurement with the ECM and the Universal Adapter connected to the circuit as shown on the right).

Idle Air Actuator Valve - Testing





^ The Idle Air Actuator Valve and air circuit (passage ways) should be checked for physical obstructions. Visually inspect the sealing gasket, mounting bracket and air hose clamps.
^ The resistance of the valve winding should be checked
^ The ECM output and Idle Speed Control Valve operation can be tested by Component Activation on the DISplus/ GT1 .
^ The Pulse Width Modulation ground outputs from the ECM can be tested using the DISplus/GT1 Oscilloscope.
^ Consult Technical Data for specified idle speed.

NOTE: If the valve is blocked or contaminated, an HEM fault code can also be present.

Air Temperature Signal Testing








The HEM contains an integral air temperature sensor. NTC sensors decrease in resistance as the temperature rises and vice versa. The ECM monitors the sensor voltage which varies as temperature changes the resistance value. For example, as temperature rises:
^ Resistance through the sensor decreases.
^ Voltage drop across the sensor decreases.
^ Input signal voltage also decreases (50v).
This sensor should be tested using:
^ DISplus/GT1 Status Page
^ DISplus/GT1 Multimeter (ohms)

Hot-Film Air Mass Sensor





This component is nonadjustable and tampering is not permitted. A faulty Hot Film Air Mass Sensor can produce the following complaints:
^ Difficult To Restart When Engine Is Hot
^ Engine Starts Then Stalls
^ Malfunction Indicator Light Illuminated
^ Engine Starts and Runs Only With Accelerator Pedal Depressed





Testing: The Hot Film Air Mass Sensor can be tested with the following methods:
^ DISplus/GT1 Fault Code and Component Testing.
^ DISplus/GT1 Status Page
^ DISplus/GT1 Oscilloscope which requires taking the measurement with the ECM and the Universal Adapter connected to the circuit (engine running).

NOTE: Visually inspect the sensor for damaged, missing or blocked screens. The screens affect air flow calibration. Also inspect the sealing rings where the sensor inserts in the air filter housing and intake boot. Ensure the pin connections are tight.