Severity: Moderate Code type: Generic (all makes)

P0606 Code: Control Module Processor Fault

The engine computer failed its own internal self-test – check its power and grounds before replacing it.

At a glance

Severity: Moderate

Meaning: Control Module Processor Fault
System: ECU & Outputs · Powertrain
Safe to drive?: With caution
Typical repair cost: $80–$1,800
DIY difficulty: Hard

Modern engine computers constantly check themselves: memory checksums, a watchdog that confirms the software is running, and on drive-by-wire engines a second processor that cross-checks throttle calculations. P0606 means one of those internal checks failed. A genuinely failed ECM is possible, but low or unstable supply voltage, a poor ground, water in a connector or corrupted software can trigger the exact same code. Condemn the ECM only after power, grounds and connectors check out, because a replacement usually has to be programmed to the vehicle and immobilizer.

Can I keep driving? Drive cautiously and get it diagnosed soon – depending on the vehicle, P0606 can bring on reduced power, stalling or a no-start without warning. If the engine drops into limp mode or stalls repeatedly, have it towed.

How to read P0606

P Powertrain
0 Generic (SAE)
6 Computer & outputs
06 Specific fault

Symptoms

Check engine light, sometimes with a wrench or reduced-power light
Reduced engine power or limp mode
Intermittent stalling or no-start
Sluggish or no response to the gas pedal
Erratic shifting because the transmission receives bad data
Code appeared right after battery work or a jump start

Possible causes

Ranked by how often each cause is behind this code (editorial estimate).

Low or unstable supply voltage from a weak battery or charging fault 25%
Poor ECM ground or high resistance in its power feed 20%
Internal ECM hardware failure 20%
Software fault that needs a reflash or calibration update 12%
Water intrusion or corrosion at the ECM connector 10%
Electronic throttle fault detected by the ECM's monitoring processor 8%
Voltage spike from a bad jump start or welding on the vehicle 5%

Diagnosis step by step

Record all codes and freeze frame
Save everything before clearing. P0606 together with P0562 or U-codes points to supply problems; together with throttle codes it points to the electronic throttle system.
Tools: OBD-II scanner
Test battery and charging system
Confirm about 12.6 V at rest and roughly 13.5–14.8 V running, and have the battery load-tested. Fix any charging problem first and recheck before going further.
Tools: Multimeter
Check ECM power and grounds under load
Back-probe the ECM power and ground pins using the wiring diagram and do voltage-drop tests while cranking. More than a few tenths of a volt on a ground is too much; clean and tighten engine and body ground straps.
Tools: Multimeter, Screwdriver
Inspect the ECM and its connectors
Look for water trails, green corrosion, pushed-back or bent pins. ECMs mounted low or near the cowl can take on water from clogged drains or a leaking windshield seal.
Tools: Flashlight
Check for software updates
A dealer or well-equipped independent shop can check whether a newer calibration exists for your ECM. Some processor faults are resolved by a reflash alone.
Tools: OBD-II scanner
Clear, retest, then decide
Clear the code and drive through the freeze-frame conditions. If P0606 returns immediately with verified good power and grounds, the ECM is likely faulty; repair or replacement must include VIN and immobilizer programming.
Tools: OBD-II scanner

Where the parts are

Charging system and control modules

1Battery
2Alternator
3Engine computer (ECM)
4CAN bus
5Transmission
6Wheel speed sensor
7High-voltage battery

Repair options & costs

Repair	DIY?	Estimated cost
Replace weak battery	Yes	$150–$350
Repair ECM ground or power circuit	No	$80–$300
ECM software reflash	No	$100–$250
Mail-in ECM repair service plus reinstall	No	$250–$600
Replace ECM with programming	No	$600–$1,800

Rough US estimates for parts and labor; shop rates vary by region. Not a quote.

Notes by brand

Ford

On many Fords with electronic throttle control, P0606 shows up alongside the wrench light and reduced power, and the root cause is often the electronic throttle body or its wiring rather than the PCM itself. Test the throttle system before replacing the PCM.

P0606 on Ford in detail

Field data

Ford	10
Chevrolet	8	Silverado 1500, Equinox, Impala
Toyota	2	Corolla, RAV4

Source: NHTSA Complaints API (US government open data), analyzed by DTC mention.

Related codes

Often appears together with

P0562 Powertrain The engine computer sees too little supply voltage – usually a charging, battery or ground… Moderate U0100 Network Another module stopped hearing from the engine computer on the CAN network. High P2135 Powertrain The two position signals inside the throttle body disagree, so the PCM can no longer trust… Moderate P0032 Powertrain The bank 1 upstream heater circuit looks shorted to power or is drawing far too much current. Low P0038 Powertrain The heater circuit of the sensor behind the bank 1 converter shows a short to power or excess… Low P0200 Powertrain The ECU found a fault in the injector control circuits that it can't pin on one cylinder, often… High P0203 Powertrain The ECU sees no normal electrical response from injector 3: its coil, its wiring or its driver… Moderate P0601 Powertrain The engine computer's stored software failed its checksum test at start-up – usually a reflash… Moderate P0604 Powertrain The engine computer's working memory failed a read/write test – rarely a software issue, often… Moderate P0605 Powertrain The memory holding the engine computer's program failed its integrity test – try one reflash… Moderate P0607 Powertrain A general internal performance check in the engine computer failed – supply, grounds… Moderate P061B Powertrain The ECM's safety monitor disagreed with its own engine torque calculation – often bad input… Moderate

Emissions / smog test impact

Will fail

P0606 turns on the check engine light, so the vehicle fails an OBD smog check. A new or reflashed ECM starts with incomplete readiness monitors, so drive normally for several days before testing.

Frequently asked questions

Does P0606 always mean a bad computer?

No. The code means an internal self-check failed, and low voltage, bad grounds, corrosion or software can all cause that. Many shops fix P0606 with a ground repair, battery or reflash; replacing the ECM is the last step, not the first.

Can I install a used ECM from a salvage yard?

Usually not plug-and-play. The module must be programmed with your VIN and paired to the immobilizer, or the engine may not start. Some rebuilders can transfer the data from your original unit onto a replacement.

Why did P0606 appear after I jump-started the car?

A voltage spike or a momentary reversed connection can upset or damage the processor. Clear the code with a healthy battery connected; if it stays away, no harm done, but if it returns immediately the module may be damaged.

Is it safe to keep driving with P0606?

Some cars run normally for weeks, others stall or go into limp mode without warning. Because the processor also watches throttle control, treat it as urgent and avoid highway trips until it's diagnosed.

Sources

SAE J2012 – Diagnostic Trouble Code Definitions
ISO 15031-6 – Road vehicles, diagnostic trouble code definitions (EOBD)
Manufacturer public service information (cross-checked)
NHTSA Complaints API
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