P0605: Internal Control Module ROM Error (Meaning, Causes, Fixes)
What P0605 means
The powertrain control module (PCM, also called the ECM) is the computer that runs the fuel, ignition and, on many vehicles, transmission systems. RepairPal explains that the PCM regularly runs a self-diagnosis where it performs normal calculations, and if the results aren't as expected it sets P0605. The ROM stores all of the PCM's operating system software, so if it fails its self-test the computer can't be trusted to do its job accurately. OBD-Codes.com describes it the same way: the PCM has detected an internal fault in its ROM. The code is generic to OBD-II vehicles (1996 and newer), but repair steps vary by make and model. OBD-Codes.com says it is more commonly found on Ford and Nissan vehicles, and search interest shows people look it up most for Ford (including the F-150 and 7.3 Powerstroke), Nissan, Hyundai, Kia, Infiniti and Ram 2500, so check technical service bulletins (TSBs) for your vehicle.
Severity: can I keep driving?
Stop and fix promptly
Get it checked right away. RepairPal rates P0605 'Urgent', meaning immediate action is needed because it can cause severe damage or put people at risk. OBD-Codes.com lists stalling and no-start among the possible symptoms, and RepairPal mentions dying when coming to a stop and poor shifting. If the engine stalls, runs badly or the transmission won't shift properly, stop driving and have it towed rather than risk losing power in traffic.
Common symptoms
- Check engine light on
- Other warning lights on the dash, such as the ABS or traction control light (both sources)
- Stalling, including dying when coming to a stop (both sources)
- Engine won't start (OBD-Codes.com)
- Poor performance, misfire-like running or improper shifting (RepairPal)
- Lower fuel economy (RepairPal)
- Failed emissions inspection (RepairPal)
- In unusual cases, no noticeable symptoms (RepairPal)
Likely causes
Roughly most to least common, based on the sources below. Your vehicle may differ.
- An internal fault in the PCM's ROM (both sources)
- Lack of proper voltage or ground to the PCM, or a bad PCM ground circuit (RepairPal; OBD-Codes.com also says to check power and ground)
- A shorted PCM-controlled output device, such as a solenoid or relay the PCM drives (RepairPal)
- An aftermarket performance programmer (OBD-Codes.com)
- PCM software that needs an update, which a flash can fix in some cases (OBD-Codes.com)
Diagnostic steps you can do
Work on a cool engine, parked on level ground with the parking brake set. Never work under a car supported only by a jack.
- Read all stored codes and freeze frame data and write them down. RepairPal says to record them and try to duplicate the conditions on a test drive, watching engine load, throttle position, RPM and road speed, because P0605 can be hard to catch.
- Check the battery and charging system, and make sure the battery terminals and ground cables are clean and tight.
- Look over the wiring and connectors at the PCM for damage or corrosion.
- If you've installed a performance programmer or tuner, consider returning the PCM to the factory calibration.
- Look up TSBs for your vehicle for a PCM software update (reflash) that addresses P0605.
Typical fixes
- Reflash the PCM with updated factory software if a TSB or update applies (OBD-Codes.com)
- Repair poor power supply or ground connections to the PCM
- Replace a shorted PCM-controlled output device found during diagnosis (RepairPal)
- Remove an aftermarket performance program
- Replace and program the PCM, or have it repaired by a specialist shop, if it has failed (OBD-Codes.com calls replacement the most likely repair)
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
- RepairPal lists two common misdiagnoses: replacing the PCM when the root cause is improper voltage to it, or when the root cause is defective PCM ground circuits. It also says to check for shorted output devices before replacing the PCM.
- A replacement PCM usually has to be programmed with the VIN and, on many vehicles, anti-theft information (for example Ford PATS), which OBD-Codes.com says can need special tools. It recommends a shop that can program the new PCM.
- OBD-Codes.com notes that this repair may be covered under the emissions warranty, possibly beyond the bumper-to-bumper or powertrain warranty, so check with your dealer.
- The sources lean differently: OBD-Codes.com calls PCM replacement the most likely repair once updates and wiring are ruled out, while RepairPal stresses that in many cases the PCM simply isn't getting clean, consistent 12-volt power and ground.
Where to buy
Plain search links. Always match parts to your exact year, make, model and engine.
FAQs
Can I drive with P0605?
It's not a good idea. RepairPal rates P0605 'Urgent', and both sources list stalling among the possible symptoms. Have it diagnosed soon, and tow it if the engine stalls or runs badly.
Does P0605 mean I need a new PCM?
Often, but not always. OBD-Codes.com says to check for a software update and the PCM's power and ground first, and RepairPal says replacing the PCM when the real problem is voltage or ground is a common misdiagnosis.
Is P0605 covered by warranty?
It may be. OBD-Codes.com says the repair may be covered by the emissions warranty, sometimes beyond the regular warranty period, so ask your dealer.
What codes are related to P0605?
OBD-Codes.com lists the other internal control module codes P0601 (memory check sum), P0602 (programming error), P0603 (keep alive memory) and P0604 (RAM).
Sources
Last reviewed 2026-10-26. Code definitions and repair steps can vary by manufacturer. Confirm with your vehicle's service information.