# P0606: Control Module Processor **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-$2,000 - **Urgency:** This week - **Most likely:** Engine computer, power, or ground fault - **DIY?:** Battery and ground checks ## Quick answer P0606 means the engine computer found a fault in its own processor during an internal self-test. Many computers have a second processor that double-checks the first, especially for electronic throttle control, and P0606 sets when those checks fail. It can come from a failing computer, a power or ground problem, or software, and some cars go into reduced power mode. ## What does P0606 mean? The processor is the part of the engine computer that runs its program, reading sensors and deciding fuel, spark, throttle opening, and often shift timing many times a second. Because a processor error could open the throttle when it should not, most modern computers include a monitoring processor or watchdog circuit that constantly checks the main processor's calculations and timing. P0606 sets when one of those internal checks fails, such as the two processors disagreeing, the watchdog not getting a timely answer, or the processor failing a test of its own memory or math. The exact tests vary widely by maker and are not published in detail. Most vehicles turn on the check engine light right away, and many limit throttle opening, called reduced power or limp mode, to keep the car controllable. "Control module" usually means the engine computer, though a transmission computer can set P0606 too. ## What are the symptoms of P0606? - Check engine light on, sometimes with a reduced power or wrench light - Reduced power mode with a slow, limited throttle - Stalling, or an engine that cranks but will not start - Hard or erratic shifting on some vehicles - Problems that come and go with heat, rain, or bumps ## What causes P0606? Ranked from most to least likely. Check them in this order: the cheap, common causes first. 1. **Internal engine computer failure** (most common). Heat, vibration, age, and moisture can damage the processor or the components around it, and the self-test catches the resulting errors. Failures often begin intermittently, showing up only when hot or on rough roads before becoming constant. A shop settles on this cause only after power, ground, and software checks pass, because a new computer is the costliest fix. 2. **Poor power or ground to the computer** (common). The processor needs stable voltage to work properly. A corroded ground strap, a loose battery terminal, a weak battery, or a failing alternator can cause voltage dips that make the self-test fail on a computer that is actually healthy. Voltage drop testing on the power and ground circuits while the engine runs usually finds this. 3. **Software fault needing an update** (common). Some makers have released updated software for computers that set P0606 falsely or under specific conditions, often described in a technical service bulletin. A dealer or well-equipped independent shop can compare the calibration in your computer with the latest release. When an update exists, reflashing costs far less than new hardware and should be tried first. 4. **Shorted sensor or throttle circuit** (less common). On some vehicles, a shorted sensor reference circuit or a fault in the electronic throttle body can make the processor checks fail, because both processors watch throttle and pedal data. Other throttle or sensor codes stored with P0606 point here. Unplugging suspect sensors one at a time while watching the code can isolate the shorted part. 5. **Water damage to the computer** (less common). Computers mounted low in the engine bay, under a leaking windshield cowl, or beneath carpet that gets wet are exposed to moisture. Corroded connector pins cause erratic signals, while moisture on the circuit board can make the processor fail its self-test only in wet weather. Either problem usually means a replacement computer once the leak is fixed. ## How do you diagnose P0606? 1. Read codes in every module and note any throttle, sensor, or voltage codes stored with P0606. 2. Test the battery and charging system, then voltage-drop test the computer's power and ground circuits. 3. Check for technical service bulletins and software updates for your VIN. 4. Inspect the computer connector and case for water or corrosion, and look for shorted sensor circuits. 5. Replace and program the computer only after power, ground, and software checks pass. ## How do you fix P0606, and what does it cost? | Fix | Typical cost | What it involves | | --- | --- | --- | | Clean or repair grounds and connections | $100-$350 | Often the cheapest fix when voltage drop testing finds a problem. | | Software update (reflash) | $100-$300 | When the maker has released an updated calibration. | | Replace and program engine computer | $600-$2,000 | Includes VIN programming; some vehicles also need throttle or immobilizer setup. | Full price breakdowns: [car battery replacement cost](/cost/car-battery-replacement). ## Is it safe to drive with P0606? > **Drive to a shop this week.** Drive only if the engine runs normally, and get it checked soon. P0606 can cause reduced power or stalling without warning, which is risky in traffic or on the highway, so stop driving and arrange a tow if the car stalls or goes into reduced power mode. ## Will P0606 fail an emissions test? P0606 turns on the check engine light, so the car fails an OBD-II emissions test in most states. A computer with an intermittent processor fault may also drop communication with the test equipment. Clearing the code resets the readiness monitors, and P0606 usually returns quickly, so repair it before testing. ## After the repair: clearing P0606 After the repair, clear codes in all modules and complete any relearns the vehicle needs, such as throttle body, idle, or immobilizer setup with a new computer. Then drive in the conditions that set the code, such as hot weather or rough roads. If P0606 stays away for a week or two and power is normal, the fix worked. ## How to prevent P0606 - Keep battery terminals clean and tight, and replace the battery when testing shows it weak. - Have ground straps checked during other work, especially on older vehicles in road-salt states. - Ask about computer software updates during dealer visits or when the engine behaves oddly. - Fix windshield cowl and sunroof drain leaks before water reaches modules or wiring. - Use proper jump-start procedures, and never use a booster set to the wrong voltage. ## Codes often seen with P0606 - [P0601](/codes/p0601): Internal Control Module Memory Check Sum Error - [P0562](/codes/p0562): System Voltage Low - [P0121](/codes/p0121): Throttle/Pedal Position Sensor/Switch "A" Circuit Range/Performance ## Frequently asked questions ### Can I drive with a P0606 code? You can sometimes drive carefully to a shop, but P0606 is less predictable than most codes. The processor fault can cause reduced power or stalling without warning. Avoid highways and long trips, and if the engine stalls or enters reduced power mode, stop when safe and have the car towed. ### What is the difference between P0601 and P0606? P0601 means the computer found its stored software or memory damaged, which a reflash may fix. P0606 means the processor failed one of its running self-tests, such as two processors disagreeing. Both point to the computer, and both call for power, ground, and software checks before replacing it. ### Does P0606 mean my engine computer is bad? Not necessarily, although it often does. Low voltage, a bad ground, a software fault, or a shorted sensor circuit can make a healthy computer fail its self-test. A shop should test power and grounds, check for software updates, and look for other codes before quoting a new computer. ### How much does it cost to fix P0606? Most P0606 repairs cost $100 to $2,000 at an independent shop. Ground or connection repairs run about $100 to $350 and a software update $100 to $300. Replacing and programming the engine computer usually costs $600 to $2,000, more on vehicles that need immobilizer or key setup. ### Why is my car in reduced power mode with P0606? Reduced power mode limits how far the throttle opens so the car stays controllable if the computer cannot trust its own processor. Because throttle control is safety-critical, many vehicles do this automatically with P0606. The car may crawl at low speed, so get off busy roads and have it checked. ### Can a bad battery cause P0606? Yes, on some vehicles low or unstable voltage can make the processor fail its self-test. Dim lights, slow cranking, a recent jump-start, or P0562 stored alongside it are clues. Test and fix the battery and charging system first, then clear the code and see if it returns before buying a computer. ### Can I fix P0606 myself? You can do the early checks: test the battery, clean and tighten the terminals, inspect ground straps, and look for water near the computer. Reflashing or programming a replacement computer needs factory software and a capable tool, so that part usually goes to a dealer or a well-equipped independent shop. ### Will a software update fix P0606? Sometimes. Makers have released updated software for computers that set P0606 under certain conditions, often listed in a technical service bulletin for specific models. A shop can compare your computer's calibration with the latest version. If no update exists or the code returns afterward, the problem is usually hardware, power, or wiring. ### Is P0606 covered by warranty? Often, on newer vehicles. The engine computer is generally covered by the federal emissions warranty for 8 years or 80,000 miles on US vehicles, and the maker's powertrain warranty may also apply. Check NHTSA for recalls by VIN and ask a dealer about bulletins before paying for a computer. ### Why does P0606 come and go? An intermittent P0606 often points to a connection, ground, or heat-related fault, since the self-test fails only when conditions are just wrong. Note when it happens, such as hot weather, bumps, or rain. That pattern helps a shop find a loose ground or water leak before replacing the computer. ## 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) - [NHTSA: Check for recalls by VIN](https://www.nhtsa.gov/recalls) ## Other computer and outputs codes - [P0562 System Voltage Low](https://diagxcar.com/codes/p0562) - [P0601 Internal Control Module Memory Check Sum Error](https://diagxcar.com/codes/p0601) ## Symptoms - [Why does my car stall while driving?](https://diagxcar.com/symptoms/car-stalls-while-driving) - [Why does my car crank but not start?](https://diagxcar.com/symptoms/car-cranks-but-wont-start) - [Why does my car lose power when accelerating?](https://diagxcar.com/symptoms/car-loses-power-when-accelerating) ## Repair costs - [Car battery replacement cost](https://diagxcar.com/cost/car-battery-replacement): $150-$450 --- Source page: https://diagxcar.com/codes/p0606 Updated: 2026-11-03 General information, not a substitute for a qualified mechanic.