This 2011 Ford Fiesta was towed to our shop with a No-Start problem.
We pushed the vehicle into our shop, and our Ford technician performed a few basic tests. With the key switched on, the instrument panel displayed a Check Engine Warning light, and the starter motor would not engage or crank the engine. We jumped the battery with a known good battery, but there was no change.
We contacted the owner for permission to continue diagnosing the engine's no-crank no-start problem.
In This Article
Symptoms
Diagnosis
Repair
FAQ
Recommended Shop
Reviews
Common Symptoms of a Bad PCM
A failing Powertrain Control Module (PCM) can display symptoms ranging from changes in vehicle behavior to more serious mechanical and electrical issues.
Identifying Signs of PCM Failure
Here are the top symptoms related to PCM failure:
Check Engine Light Activation: The check engine light often indicates a PCM problem, especially when it appears after a failed self-diagnostic.
Decreased Fuel Efficiency: A PCM regulates the engine's air-fuel mixture. If the vehicle’s fuel efficiency decreases unexpectedly it could be due a malfunctioning PCM.
Difficult or Irregular Shifting: The PCM can also control the transmission, and shifting problems or irregularities can be caused by a malfunctioning PCM.
Emission Test Failure: The PCM plays a large role in minimizing vehicle engine emissions. A malfunctioning PCM could cause an emission test failure.
Engine Misfires or Backfires: A malfunctioning PCM can disrupt the engine fuel-air mixture leading to engine misfire or backfire. This serious issue can damage the engine if not repaired promptly.
Engine Stalling or Hesitation: A defective PCM can cause your vehicle’s engine to stall or hesitate. This can pose safety risk while driving and requires immediate attention.
Ignition Issues: The PCM is crucial to your vehicle’s ignition system. Difficulty starting, particularly in colder months, or no-start problems, could be due to weak ignition spark caused by a faulty PCM.
Inability to Connect Scan Device: The PCM is the main component in communicating vehicle diagnostic information. If a scan tool has difficulty connecting to or returning information from the PCM, this could be a sign of a PCM problem.
PCM-Related Error Codes: A diagnostic scan of your vehicle can reveal PCM-specific error codes indicating a malfunctioning PCM.
PCM issues require detailed, careful diagnostic testing. The engine management system is very complex and requires a high level of technician skill to diagnose a PCM problem. The PCM unit is expensive and may be damaged if the cause of the PCM failure is not found and corrected before PCM replacement.
State Street Auto Service has highly skilled technicians who are experienced with PCM and electronic engine control diagnostics. Contact us if you need help with your vehicle.
Diagnosis
Our diagnosis of any problem follows a series of steps that lead to the cause of the problem. Electrical issues can have multiple causes and must be investigated in a specific, step-by-step order.
Sometimes, electrical problems are complex and must be diagnosed and repaired in specific steps as each symptom is investigated and resolved. These multiple steps of diagnosis and repair, each one in greater depth and requiring additional time to investigate and repair, are billed in stages. Each time, progress is reported to the vehicle owner, and permission to do further diagnosis and repair is requested.
In the first stage of the diagnosis, our technician visually inspected the vehicle for obvious mechanical and electrical problems. Next, they used a scan tool to check for OBD error codes (see photos).
The technician found that the scanner could not communicate with the Powertrain Control Module (PCM). All other vehicle control modules had normal communications with the scanner. The technician cleared all stored error codes, ran a test related to the PCM, and found multiple error codes. Then, they checked the electrical fuses and related wiring, pinpoint testing of each connection. No fuse or wiring problems were found.
At this point, the technician needed additional diagnostic time, and the customer was contacted with an update on the repair.
An example of the 2011 Ford Fiesta's OBD scanner error codes. There were 10 errors in total. The two most important error codes were the low battery voltage and the PCM Lost Communication. Other error codes were related to PCM communication problem. This hinted to the primary problem being with the PCM unit.
Diagnostic Testing Stage Two
Our technician performed additional pinpoint testing, searching for why the PCM was not communicating with the scanner. The wiring to and from the PCM was tested for resistance, and all were found to be within specifications. Next, the electrical connectors were inspected for corrosion or bent connector pins, but no problems were found with the wiring. Then, the PCM was tested for correct electrical grounds, and all were found to be within specifications. This pinpoint testing led the technician to the conclusion that the PCM unit had failed and needed to be replaced.
The vehicle owner was contacted and given an estimate for the PCM replacement, along with a caution that additional testing and/or repairs may be needed once the PCM is replaced. The repair was approved, and the technician continued with the PCM replacement.
Repair
Powertrain Control Module Replacement
Our Ford technician removed the components required to access and remove the PCM power control module. The Ford dealer supplying the new PCM unit programmed it with the vehicle's VIN number. The new PCM was installed in the vehicle, and components removed during repair were reassembled.
Once the new PCM was installed, the PCM error code storage was cleared, and a scan test was done to verify the PCM communication was working and that the no-crank, no-start issue was resolved. The technician road-tested the vehicle to confirm that all PCM-related problems had been fixed.
The technician did a final quality control inspection and returned the vehicle to our happy customer.
FAQ
Does a PCM need to be reprogrammed?
When a PCM is replaced, it must be programmed to match the vehicle. The vehicle dealership that supplies the new unit will program the new replacement PCM.
What Causes PCM Failure?
The powertrain control module may experience failure due to corrosion of electrical connections, broken or damaged wires, other engine management system components, or failed electronic components inside the PCM itself. A common cause of PCM failure is power surges or spikes produced by jump-starting, damaged vehicle wiring, or a faulty alternator.
Recommended Ford Repair Service Shop Near Ann Arbor, MI
Contact State Street Auto Service for all Ford service and repair in the Ann Arbor, Michigan area. Our Ford technicians have the skill and experience to diagnose and repair your Ford problems correctly. We are Ford service specialists.
You can trust your Ford service to State Street Auto Service. Located in Whitmore Lake, MI, State Street Auto Service also serves the surrounding areas, including Ann Arbor, MI; Pittsfield, MI; Ypsilanti, MI; Saline, MI; and Dexter, MI.