Analyzing Powertrain Control Module (PCM) Data

ANALYZING POWERTRAIN CONTROL MODULE (PCM) DATA

Various Data Procedures
Once the fault area is identified, the circuit must checked to determined 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 the sensor receives and responds to changes.
1. Access, monitor, and record the appropriate sensor PID(s).
2. Create the condition or cause the condition to change.
3. If the value changes appropriately, then it should be operating OK.

Examples:
- View the engine oil temperature (EOT) PID while the engine warms.
- It should change from a higher voltage (2.6 volts) for a cold engine, to a lower voltage as the engine warms (0.6 volts).
- Apply and release the accelerator pedal while monitoring the accelerator pedal position (APP) PID for a change of state.
- Apply and release the brake pedal while monitoring the brake pedal position (BPP) PID for a change of state.

Change Input and Verify Output Response
The purpose is to verify how the PCM and actuator circuit responds to sensor input.
1. Access and monitor the appropriate sensor PID(s).
2. Create the condition to cause the input condition to change.
3. Monitor the change (response) in the actuator PID or the actuator signal circuit with a measuring device.

Example:
- Increase the accelerator pedal position under load, and observe the RPM DSD PID and circuit change.

Coil Resistance (Solenoids/Relays)
The purpose is to measure the resistance value of the device.
1. Key OFF.
2. Disconnect the component from the vehicle harness.
3. Using an ohmmeter, measure across the component terminals in question.

Harness Opens
The purpose is to check the harness for open circuits.
1. Key OFF.
2. Disconnect the component from the vehicle harness.
3. Disconnect the appropriate PCM harness.
4. Using an ohmmeter, isolate the circuit in question from the harness pin to the component connector signal pin.
5. The resistance value should be less than 5 ohms.

Harness Shorts
The purpose is to check the harness for short circuits (to ground or voltage).
1. Key OFF.
2. Disconnect the component from the vehicle harness.
3. Using an ohmmeter, measure the resistance between the signal circuit and signal return circuit, power ground circuit, VREF circuit, or vehicle power.
4. If the resistance value is less than 10,000 ohms, the 2 circuits are shorted.