Analyzing PCM Data

ANALYZING PCM DATA

Various Data Procedures
Once the fault area is identified, the circuit must be checked to determine if the wiring or component is at fault. Use any of the following methods to diagnose a suspected PCM wire circuit or device. Some methods are particular to a certain type of PCM device.
- Change Condition to Cause Response by Input
- Change Input and Verify Output Response
- Click Testing/Output State Control
- Coil Resistance (Solenoids/Relays)
- Harness Opens
- Harness Shorts

Change Condition to Cause Response by Input
The purpose is to verify sensor receives and responds to changes.
1. Select, view and record the appropriate sensor PID(s).
2. Create condition or cause condition to change.
3. If reading changes appropriately, then it should be operating OK.
Examples:
- View EOT PID while engine warms up.
- It should change from a higher voltage (2.6V) for a cold engine, to a lower voltage as the engine warms up (0.6V).
- Move accelerator pedal, observe APP PID change.
- Press brake pedal, watch BOO PID change states.

Change Input and Verify Output Response
The purpose is to verify how the PCM and actuator circuit responds to sensor input.
1. Select, view the appropriate sensor PID(s).
2. Create condition to cause input condition to change.
3. Observe change (response) in actuator PID or actuator signal circuit measured by a measuring device.
Example:
- Increase accelerator pedal position under load, observe RPM DSD PID and circuit change.

Coil Resistance (Solenoids/Relays)
The purpose is to measure the correct resistance value of device.
1. Key off.
2. DLC disconnected, from any scan tools.
3. Disconnect the component from vehicle harness.
4. Using an ohmmeter and referencing the Static Resistance Value Chart, measure across the component terminals in question.

Harness Opens
The purpose is to check harness for open circuits
1. Key off.
2. DLC disconnected from any scan tools.
3. Disconnect the component from the harness.
4. Disconnect the appropriate PCM harness.
5. Using an ohmmeter, isolate the circuit in question from the harness pin to the component connector signal pin.
6. Reading should be less than 5 ohms.

Harness Shorts
The purpose is to check harness for short circuits (to ground or power).
1. Key off only.
2. DLC disconnected from any scan tools.
3. Disconnect the component from vehicle harness.
4. Using an ohmmeter, measure the resistance between the signal circuit and signal return circuit, power ground circuit, VREF circuit or vehicle power.
5. If reading is less than 5 ohms, then the two circuits are shorted.