Failed PCM/ECM (both sources call this the most likely cause). Outdated PCM software that a reflash may fix in some cases (OBD-Codes.com). Bad PCM wiring or connections (RepairPal). Bad PCM ground circuits (RepairPal). Shorted or faulty PCM-controlled output devices; RepairPal says to check these before replacing the PCM because they can cause the processor to fail. CAN bus communication problems (RepairPal).

Reflash (update) the PCM software, which OBD-Codes.com says can fix it in some cases. Repair PCM wiring, connectors or ground circuits (RepairPal). Repair a shorted output device before installing a new PCM, so it doesn't damage the replacement (RepairPal). Replace the PCM, the most common fix per both sources; the new unit must be programmed to the vehicle, which can include the VIN and anti-theft information (OBD-Codes.com).

P0606🔧 Engine computer (PCM/ECM)Stop and fix promptly

P0606: Control Module Processor Fault (Meaning, Causes, Fixes)

Q: What does P0606 mean?

P0606 means the engine computer (PCM or ECM) failed its own internal self-check. Both OBD-Codes.com and RepairPal say the computer itself is the most likely cause, but a software update (reflash), bad PCM wiring, connectors or grounds, a shorted output device or a CAN bus communication problem should be ruled out before replacing it. The powertrain control module (PCM), also called the engine control module (ECM), manages the fuel and ignition systems and, on many vehicles, the transmission and other systems. RepairPal explains that it regularly runs a self-diagnosis in which it performs normal calculations; if the results aren't as expected, it sets P0606. OBD-Codes.com describes it as the PCM detecting an internal integrity fault. RepairPal names the code Control Module Processor; OBD-Codes.com calls it PCM / ECM Processor Fault. Related codes P0600 through P0610 cover other control module faults, such as memory errors (P0603 to P0605) and control module performance (P0607).

Q: Can I keep driving with P0606?

Stop and fix promptly. Get it checked soon. RepairPal rates P0606 Urgent and lists stalling when coming to a stop, misfire-like symptoms and poor shifting among the possible symptoms. OBD-Codes.com is calmer and says the check engine light is most likely the only symptom. Because the engine computer runs fuel, ignition and often the transmission, don't ignore it, and an open code can also fail an OBD2 emissions inspection.

Reviewed 2026-10-22 · Based on 2 cited source(s)

What P0606 means

The powertrain control module (PCM), also called the engine control module (ECM), manages the fuel and ignition systems and, on many vehicles, the transmission and other systems. RepairPal explains that it regularly runs a self-diagnosis in which it performs normal calculations; if the results aren't as expected, it sets P0606. OBD-Codes.com describes it as the PCM detecting an internal integrity fault. RepairPal names the code Control Module Processor; OBD-Codes.com calls it PCM / ECM Processor Fault. Related codes P0600 through P0610 cover other control module faults, such as memory errors (P0603 to P0605) and control module performance (P0607).

Severity: can I keep driving?

Stop and fix promptly

Get it checked soon. RepairPal rates P0606 Urgent and lists stalling when coming to a stop, misfire-like symptoms and poor shifting among the possible symptoms. OBD-Codes.com is calmer and says the check engine light is most likely the only symptom. Because the engine computer runs fuel, ignition and often the transmission, don't ignore it, and an open code can also fail an OBD2 emissions inspection.

Common symptoms

Check engine light on (both sources; OBD-Codes.com says this is most likely the only symptom)
ABS or traction control light may come on (RepairPal)
Vehicle may not perform or shift properly (RepairPal)
Lower fuel economy (RepairPal)
In some cases, stalling when coming to a stop or misfire-like symptoms (RepairPal)
In unusual cases, nothing the driver notices (RepairPal)

Likely causes

Roughly most to least common, based on the sources below. Your vehicle may differ.

Failed PCM/ECM (both sources call this the most likely cause)
Outdated PCM software that a reflash may fix in some cases (OBD-Codes.com)
Bad PCM wiring or connections (RepairPal)
Bad PCM ground circuits (RepairPal)
Shorted or faulty PCM-controlled output devices; RepairPal says to check these before replacing the PCM because they can cause the processor to fail
CAN bus communication problems (RepairPal)

Diagnostic steps you can do

⚠ Before you start

Work on a cool engine, parked on level ground with the parking brake set. Never work under a car supported only by a jack.

Write down any other codes stored with P0606 and save the freeze frame data; RepairPal says this is important because P0606 can be hard to reproduce.
Check for technical service bulletins (TSBs) for your vehicle, as OBD-Codes.com recommends. A known software update may cover it.
Check whether the repair is covered by your emissions warranty; OBD-Codes.com notes it may be covered beyond the normal warranty period.
Make sure the battery terminals and engine grounds are clean and tight, and look over the PCM connectors for corrosion or damage.
OBD-Codes.com says there is little an owner can do beyond this; the rest needs a shop with programming tools.

Typical fixes

Reflash (update) the PCM software, which OBD-Codes.com says can fix it in some cases
Repair PCM wiring, connectors or ground circuits (RepairPal)
Repair a shorted output device before installing a new PCM, so it doesn't damage the replacement (RepairPal)
Replace the PCM, the most common fix per both sources; the new unit must be programmed to the vehicle, which can include the VIN and anti-theft information (OBD-Codes.com)

Repair costs vary widely by vehicle, region, parts brand and shop, so we don't quote prices. Get a written estimate after diagnosis.

🛠 When to call a pro

Almost always: OBD-Codes.com strongly recommends a shop that can reprogram a new PCM
The car stalls, misfires or won't shift properly; RepairPal rates P0606 Urgent
Other control module or communication codes are stored with P0606
The repair may be under an emissions warranty, so check with your dealer first

Where to buy

Plain search links. Always match parts to your exact year, make, model and engine.

OBD2 scanners on Amazon Parts at Advance Auto Parts catalog at RockAuto

FAQs

Is P0606 serious?

It can be. RepairPal rates it Urgent and lists stalling, misfire-like symptoms and shifting problems as possible symptoms. OBD-Codes.com says that often the check engine light is the only sign. Either way, the engine computer is involved, so have it diagnosed soon.

Does P0606 always mean a bad PCM?

Usually, but not always. Both sources say a failed PCM is the most likely cause. OBD-Codes.com says a software reflash fixes it in some cases, and RepairPal lists wiring, grounds, shorted output devices and CAN bus problems as other causes to rule out.

Can I replace the PCM myself?

Generally not. OBD-Codes.com says a new PCM usually has to be programmed with the VIN and anti-theft information using special tools, and recommends a qualified shop.

Is P0606 covered by warranty?

Possibly. OBD-Codes.com notes the repair may be covered under the emissions warranty, even past the bumper-to-bumper or powertrain warranty, so check with your dealer.

Why do the sources disagree?

RepairPal rates P0606 Urgent and lists symptoms like stalling, poor shifting and an ABS or traction light; OBD-Codes.com says the check engine light is most likely the only symptom. RepairPal also lists more causes (wiring, grounds, output devices, CAN bus), while OBD-Codes.com points almost only to the PCM and mentions a reflash.

Sources

Last reviewed 2026-10-22. Code definitions and repair steps can vary by manufacturer. Confirm with your vehicle's service information.