# P0601: Internal Control Module Memory Check Sum Error **Verdict:** Drive to a shop this week Computer and outputs - Generic OBD-II code, applies to all gasoline cars and light trucks sold in the US since 1996. - **Typical cost:** $100-$1,800 - **Urgency:** This week - **Most likely:** Corrupted software or a failing computer - **DIY?:** Battery checks only ## Quick answer P0601 means the engine computer ran a self-check on its stored software and found that the memory does not add up the way it should. The program that runs the engine may be corrupted, so the car can run normally, run poorly, or refuse to start. A software reflash fixes some cases, while others need a new computer. ## What does P0601 mean? The engine computer, also called the ECM or PCM, stores its operating program and calibration in flash memory, the same basic kind of memory used in a USB drive. That calibration holds the fuel tables, spark timing, and often shift settings for your exact engine and transmission. Because a corrupted program could run the engine incorrectly, the computer protects it with a checksum, a number calculated from all the stored data. Each time the computer powers up, and on many vehicles continuously while running, it recalculates that number and compares it with the stored value. If they do not match, it sets P0601 and usually turns on the check engine light right away, without waiting for a second trip. "Internal" means the fault is inside the module itself, not in a sensor or wire. On some vehicles another powertrain module, such as the transmission computer, can store P0601 about its own memory, so the scan tool shows which module set it. ## What are the symptoms of P0601? - Check engine light on, often right after a dead battery or software update - Engine cranks but will not start, or will not crank at all - Stalling, rough running, or reduced power - Odd shifting or transmission stuck in one gear - Sometimes no change at all in how the car drives ## What causes P0601? Ranked from most to least likely. Check them in this order: the cheap, common causes first. 1. **Corrupted or outdated software** (most common). A program can be damaged by a software update that was interrupted, or if battery voltage dropped while the computer was writing data. Some vehicles also have known software faults that makers fix with an updated calibration. Because the hardware is fine in these cases, a successful reflash with the correct factory software often clears P0601 for good. 2. **Failed memory inside the computer** (common). Heat cycles, vibration, and age can damage the memory chip or the circuit board around it. Once the hardware is bad, a reflash will not hold, fails partway through, or the code returns within days. Computers mounted near the engine or in hot, damp spots are more exposed. A shop usually reaches this verdict after a reflash attempt fails. 3. **Low voltage, bad grounds, or a jump-start spike** (common). A weak battery, a corroded ground strap, or a voltage spike from an incorrect jump-start or failing alternator can disrupt the computer while it reads or writes memory. Sometimes this corrupts data, and sometimes it causes a false checksum failure. Testing the battery, charging output, and module grounds comes before condemning the computer. 4. **Water or corrosion inside the module** (less common). Water can enter through a cracked case, a failed seal, a leaking windshield cowl, or a clogged drain, depending on where the computer is mounted. Corrosion on the circuit board or connector pins causes memory errors along with other strange faults. Green or white crust in the connector is a clear sign, and the module usually needs replacing. 5. **Incorrect or aftermarket programming** (less common). Aftermarket performance tunes, a used computer from another vehicle, or a reflash with the wrong calibration file can leave software that fails the checksum or does not match the vehicle. Restoring the correct factory calibration for the VIN usually fixes it. Tell the shop about any tuning, because it changes how they approach the diagnosis. ## How do you diagnose P0601? 1. Read codes in every module, note which module stored P0601, and check whether it returns right after clearing. 2. Test the battery and charging system, and check power and ground circuits at the computer. 3. Check for service bulletins and software updates for your VIN, then reflash with the latest factory calibration on a stable power supply. 4. If the reflash fails or P0601 returns, inspect the module and connector for water or corrosion, then replace and program the computer. ## How do you fix P0601, and what does it cost? | Fix | Typical cost | What it involves | | --- | --- | --- | | Reflash (reprogram) the engine computer | $100-$300 | Loads the latest factory software while a power supply holds voltage steady. | | Fix weak battery or bad grounds | $100-$400 | Needed first if low voltage caused or contributed to the fault. | | Replace and program engine computer | $600-$1,800 | Includes programming to the VIN; some vehicles also need key or immobilizer setup. | Full price breakdowns: [car battery replacement cost](/cost/car-battery-replacement). ## Is it safe to drive with P0601? > **Drive to a shop this week.** If the engine runs normally, you can usually drive carefully to a shop soon. Corrupted engine software can cause stalling or a no-start without warning, so avoid long trips and highway driving until it is checked, and stop if the car stalls or loses power. ## Will P0601 fail an emissions test? P0601 turns on the check engine light, which fails an OBD-II emissions test in most states. A computer with damaged memory may also fail to report readiness monitors or communicate properly with the testing equipment. After a reflash or replacement, the monitors start over as not ready and need normal driving to complete before a retest. ## After the repair: clearing P0601 After a reflash or a new computer, the shop clears codes in every module and runs any required relearns, such as idle, throttle, crankshaft position, or key programming. Drive normally for several days. The fix worked if P0601 does not return, the engine starts and runs normally, and the readiness monitors gradually show complete. ## How to prevent P0601 - Use a battery maintainer or support power supply whenever a computer is being reprogrammed. - Replace a weak battery before it causes low-voltage starts and corrupted computer data. - Follow the owner's manual jump-start steps, connecting the last clamp to a ground point. - Keep the cowl drains and battery area clean so water cannot reach the computer. - Avoid unverified performance tunes, and keep a copy of the factory calibration if you tune. ## Codes often seen with P0601 - [P0606](/codes/p0606): Control Module Processor - [P0562](/codes/p0562): System Voltage Low - [P0700](/codes/p0700): Transmission Control System (MIL Request) ## Frequently asked questions ### Can I drive with a P0601 code? You can often drive carefully if the engine runs normally, but plan to get it checked soon. Corrupted engine software can cause stalling or a no-start without warning. Avoid long trips and highway driving, and if the car stalls, loses power, or shifts strangely, stop driving and have it towed. ### What does checksum error mean? A checksum error means the computer added up its stored program and got a different number than it expected. That tells it the software may be damaged. The computer cannot trust a damaged program to control fuel and spark correctly, so it records P0601 and turns on the check engine light. ### Does P0601 mean I need a new engine computer? Not always, since a successful reflash with the latest factory software fixes many P0601 cases. If the reflash fails partway, the code returns, or the module shows water damage, the computer usually needs replacing. Ask the shop to try reprogramming and check bulletins before quoting a new module. ### How much does it cost to fix P0601? Most P0601 repairs cost $100 to $1,800 at an independent shop. A reflash runs about $100 to $300, and fixing a weak battery or bad ground $100 to $400. Replacing and programming the engine computer usually costs $600 to $1,800, depending on the vehicle and whether keys need programming. ### Can a dead battery cause P0601? It can. A weak battery, a bad jump-start, or a voltage drop while the computer is saving data can corrupt memory or cause a false checksum failure. If P0601 appeared right after a dead battery, test the battery and charging system first, then clear the code and see whether it returns. ### Can I fix P0601 myself? Usually not entirely, because reprogramming needs factory software, a capable programming tool, and a stable power supply. You can test the battery, clean the terminals, check grounds, and look for water around the computer. A junkyard computer almost always needs programming to your VIN before it will work. ### Can I just clear P0601? You can clear it, but if the memory is truly corrupted, P0601 usually returns at the next key-on or within minutes. Clearing also erases the freeze-frame data a shop uses to diagnose it. Write down every code before clearing, and expect the readiness monitors to reset to not ready. ### Can a used engine computer fix P0601? Sometimes, but a used computer usually must be programmed with your VIN, the correct calibration, and on many vehicles your key or immobilizer data. Without that, the engine may not start. Buy from a seller who matches the part number to your vehicle, and budget for programming at a shop. ### Is P0601 covered by warranty? Often, on newer vehicles. The engine computer is one of the major emissions parts covered by the federal emissions warranty for 8 years or 80,000 miles on most US vehicles. Coverage details vary by vehicle and state, so check your warranty booklet. Damage from water, tuning, or wiring changes may not be covered. ### Will P0601 fail an emissions test? Yes, in most states P0601 fails an OBD-II emissions test because it turns on the check engine light. A damaged computer may also fail to report readiness monitors. After the repair, drive normally for several days so the monitors complete, and check them with a scan tool before returning for the test. ## Sources - [SAE J2012: Diagnostic Trouble Code Definitions](https://www.sae.org/standards/content/j2012_201812/) - [EPA: On-Board Diagnostics (OBD)](https://www.epa.gov/state-and-local-transportation/vehicle-emissions-board-diagnostics-obd) ## Other computer and outputs codes - [P0562 System Voltage Low](https://diagxcar.com/codes/p0562) - [P0606 Control Module Processor](https://diagxcar.com/codes/p0606) ## Symptoms - [Why does my car crank but not start?](https://diagxcar.com/symptoms/car-cranks-but-wont-start) - [Why does my car stall while driving?](https://diagxcar.com/symptoms/car-stalls-while-driving) ## Repair costs - [Car battery replacement cost](https://diagxcar.com/cost/car-battery-replacement): $150-$450 --- Source page: https://diagxcar.com/codes/p0601 Updated: 2026-11-03 General information, not a substitute for a qualified mechanic.