What are the symptoms of a bad PCM on a 6.7 powerstroke?

On a Ford 6.7L Power Stroke diesel, a failing Powertrain Control Module (PCM) can trigger a range of symptoms across the engine, fuel system, and drivetrain. The most common signs include hard starting or no starting, stalling, rough idle, and a check engine light with PCM-related fault codes. Diagnosis by a professional is essential, as PCM issues often mimic problems from sensors, wiring, or fuel delivery.

What the PCM does in the 6.7 Power Stroke

The PCM in the 6.7 Power Stroke acts as the central brain for engine management, coordinating fuel injection, glow plug operation, turbo control, EGR, emissions systems, and engine timing. It communicates with numerous sensors and modules over the vehicle’s CAN bus. When the PCM malfunctions, readings can become inconsistent, leading to misfires, poor fuel economy, limp mode, or unpredictable drivability. Troubleshooting typically starts with a data scan to review live sensor data and fault codes, followed by power/ground checks and wiring inspections.

Common driveability and performance symptoms

Below is a list of the most frequently observed symptoms that suggest a PCM might be failing, or at least contributing to the issue. These signs often appear together rather than in isolation.

• Hard starting or no-start conditions that require extended cranking


• Stalling or engine dying unexpectedly while driving


• Rough idle, misfires, or fluctuating engine RPM


• Loss of power or limp mode limiting acceleration


• Inconsistent or inaccurate sensor readings feeding the engine and transmission


• Check Engine Light (MIL) with fault codes related to PCM, CAN bus, or sensor communication


• Abnormal or delayed transmission behavior, including unusual shifting patterns or timing

These symptoms can also be caused by sensor failures, wiring problems, fuel delivery faults, or transmission issues. A failing PCM, however, often presents multiple symptoms across systems and may show a pattern of intermittent or cascading failures that worsen with vehicle use.

Electrical and diagnostic indicators

In addition to drivability problems, a malfunctioning PCM frequently reveals itself through electrical symptoms and diagnostic results. This category focuses on data communication and power-supply concerns that point toward the PCM as the source.

• No communication with a diagnostic scan tool or intermittent CAN bus errors


• Diagnostic trouble codes that reference PCM/ECM or communication faults, and codes that are not easily cleared


• Parasitic battery drain or a PCM power/ground issue causing the module to stay awake or reset


• Fuses or relays related to the PCM that blow or reset due to internal faults


• Inaccurate or erratic gauge readings (fuel, boost, temperature) stemming from faulty PCM sensor interpretation


• Security/immobilizer warnings or unexpected behavior when cycling the ignition


• Susceptibility to water exposure or corrosion in PCM power/ground circuits after a flood or wash

Because these signals can also arise from wiring or sensor problems, technicians typically verify the PCM by testing power and ground integrity, checking for corrosion in the harness, and examining CAN bus continuity before concluding a PCM failure.

Testing and next steps

For suspected PCM failure, a methodical diagnostic approach helps separate the PCM from peripheral causes. Typical steps include reviewing live data from multiple sensors, checking the PCM’s power supply and ground paths, inspecting related wiring and connectors for damage or corrosion, ensuring software is up to date, and performing a controlled PCM reflash or replacement if justified by the data. Given the cost and complexity, most shops confirm PCM issues with definitive electrical tests and data logs before replacing the unit.

Summary

A bad PCM on a 6.7 Power Stroke can manifest as a combination of starting issues, stalling, misfires, loss of power, abnormal transmission behavior, and a cascade of electrical/communication faults. Because symptoms often overlap with sensor, wiring, or fuel-system problems, professional diagnostic work—centered on data analysis, power/ground checks, and CAN bus health—is essential to confirm a PCM failure and determine the appropriate remedy.

Final takeaway

If you experience multiple, cross-system symptoms—especially simultaneous drivability issues and diagnostic communication problems—it’s prudent to have the PCM tested by a qualified technician rather than replacing parts in a trial-and-error approach. A precise diagnosis not only saves money but also prevents unnecessary component replacements.

What happens when a powertrain control module goes bad?

If the engine is the heart of your car, the PCM is the brain. It's constantly making decisions to optimize how the vehicle runs. A glitch in its programming can result in poor fuel economy, rough idling, sluggish acceleration, or even failure to start.

What are the symptoms of a blown PCM?

Erratic or random stuck shifting is one of the most severe PCM failure symptoms. A faulty sensor or PCM may lead to transmission damage. Whatever the PCM issue, you must take your vehicle for service immediately. These transmission conditions can present safety concerns or even strand you.

What is the most common problem with 6.7 power stroke?

The biggest problems with the 6.7 Powerstroke include fuel system issues, such as CP4 injection pump failure (especially on pre-2020 models), and emissions system problems like clogged EGR coolers and faulty EGT or NOx sensors. Other common concerns are leaks, often from the upper oil pan or the cold-side charge pipe, and issues with the high-pressure fuel pump.
 
This video explains some of the common problems with the 6.7 Powerstroke, including injection pump failure: 48s8020 AutomotiveYouTube · Dec 27, 2022
Fuel system 

• Injection pump failure: The Bosch CP4 injection pump on pre-2020 models is a major issue. It can fail due to metal-on-metal contact, sending metal shavings throughout the fuel system and causing extensive damage to injectors, lines, and regulators. 
• Fuel filter housing: The secondary fuel filter housing can leak, particularly the plastic fuel filter housing fitting, which can also be a fire hazard if it breaks. 

Emissions system

• EGR cooler: The EGR cooler is prone to clogging from carbon deposits, which can lead to a loss of power and may eventually require replacement. 
• EGT and NOx sensors: These sensors are known to fail, which can trigger a check engine light or even cause the vehicle to shut down. The middle EGT sensors are the most common failure points. 

You can watch this video to learn more about common EGR cooler problems: 58sPower Stroke MaintenanceYouTube · May 12, 2023
Leaks and other issues

• Oil leaks: A significant number of leaks are reported, especially from the upper oil pan and front cover, often caused by a clogged crankcase filter that builds excessive pressure. 
• Charge pipe failure: The cold-side charge pipe is a common failure point that can leak, leading to a loss of boost pressure. 
• Exhaust manifold: The exhaust manifold is infamous for cracking, which can cause exhaust leaks, a ticking noise, and a loss of performance. 
• Turbocharger issues: Early models had issues with the turbocharger's ceramic ball bearings, though updates were made in later years. 

This video shows examples of Ford 6.7 Powerstroke problems, including rad leaks and EGR issues: 1mJT2JZYouTube · Mar 8, 2024

How do I know if my Ford PCM is bad?

Common symptoms of a bad Ford PCM include the check engine light coming on, engine stalling or cutting out, rough idling or misfiring, poor acceleration, and erratic shifting. Other indicators can be difficulty starting the engine or poor fuel economy. 
This video explains the top symptoms and causes of a bad PCM: 59sMechanical BoostYouTube · Apr 24, 2023
Engine and performance problems

• Stalling: The engine may suddenly stall while driving or cutting off for no apparent reason. 
• Rough idle/misfires: The engine may run roughly, sputter, or misfire, especially when accelerating. 
• Loss of power: You might experience a sudden drop in power or a lack of acceleration. 
• Difficulty starting: The vehicle may crank but have trouble starting, or it might start and then die. 

Shifting and fuel issues 

• Erratic shifting: The transmission may shift erratically, get stuck in a gear, or shift at incorrect times. 
• Poor fuel economy: A malfunctioning PCM can't accurately manage fuel delivery, leading to decreased fuel efficiency. 

Warning lights and codes 

• Check Engine Light: The check engine light is often the first sign, though other issues can also cause it to illuminate. 
• No codes: In some cases, a failing PCM might cause stalling without setting any fault codes, making diagnosis difficult without targeted testing. 

This video demonstrates how to identify a faulty PCM: 1mWrenching With KennyYouTube · May 30, 2023
How to diagnose further

• Use an OBD2 scanner to check for specific fault codes, as the PCM can cause issues without a clear code being present. 
• Inspect the PCM's wiring harness for corrosion or damage, and check for water intrusion around the module itself. 
• Consulting a professional mechanic can be helpful, especially if the issue is intermittent or difficult to diagnose, according to Consumer Protection Law Group and JustAnswer.