Here's a breakdown of how to approach checking the PCM:
1. Gather Information & Tools:
* Understand the Symptoms: What's wrong with your truck? Rough running, no start, check engine light (CEL) with specific codes, etc.? This is crucial for narrowing down the problem.
* OBD-II Scanner: This is essential. A good quality scanner that can read and clear codes, as well as display live data (PID data) from various sensors, is necessary. Generic scanners might work, but a more professional-grade one that specifically works well with Ford trucks is recommended.
* Voltmeter/Multimeter: Used to check power and ground connections to the PCM.
* Wiring Diagrams: A wiring diagram specific to your year and model is invaluable. You can find these online through repair manuals or websites specializing in Ford truck repair information.
2. Diagnostic Steps:
* Check the Batteries: A weak or failing battery can cause erratic PCM behavior. Ensure the batteries are fully charged and properly connected.
* Read and Clear Diagnostic Trouble Codes (DTCs): Connect your OBD-II scanner and read the codes. Write them down! Many codes will pinpoint the problem to a specific sensor or component *before* you suspect the PCM.
* Inspect Wiring and Connectors: Carefully inspect the wiring harness leading to and from the PCM for any signs of damage, corrosion, or loose connections. Pay close attention to the grounds. Corrosion is a frequent issue, especially in older trucks.
* Check Sensor Readings (Live Data): Use your scanner to monitor sensor data while the engine is running. Compare these readings to the specifications in your repair manual or online resources. Inconsistencies or out-of-range values could indicate a failing sensor, which may be causing the PCM to malfunction – or at least triggering codes. Common sensors to check are:
* IAT (Intake Air Temperature):
* MAP (Manifold Absolute Pressure):
* ECT (Engine Coolant Temperature):
* CMP (Camshaft Position):
* CKP (Crankshaft Position):
* Fuel Pressure:
* Check Power and Ground to the PCM: Use your voltmeter to verify that the PCM is receiving proper power and ground. This usually involves checking the fuses and relays associated with the PCM circuit, and then verifying voltage at the PCM connector itself. Consult your wiring diagram for pinouts.
* Visual Inspection of the PCM: Carefully examine the PCM itself for any signs of physical damage, overheating, or corrosion. This is unlikely, but possible.
3. Considering PCM Failure:
Only after thoroughly checking all the above should you consider PCM failure as a possibility. A failing PCM is usually indicated by a cluster of seemingly unrelated codes, or a complete failure to communicate with the scanner.
4. PCM Testing and Replacement:
* Professional Diagnosis: If you've exhausted all other options and suspect the PCM, it's best to take the truck to a qualified diesel mechanic specializing in Ford Power Strokes. They have specialized equipment for PCM testing that goes beyond what a typical OBD-II scanner can do.
* PCM Replacement (If Necessary): Replacing a PCM is a fairly involved process and often requires reprogramming or flashing the new PCM with your truck's specific information. This must be done correctly to avoid further problems.
Important Note: Incorrectly diagnosing and replacing the PCM can be expensive and time-consuming. Always start with the simplest and most likely causes first. Always double-check your work and consult your wiring diagrams!
