Lost Communication With ECM/PCM A
The U0100 code means the vehicle's onboard diagnostic system has detected: Lost Communication With ECM/PCM A. This is a critical severity code.
- Keep driving?
- No -- stop driving
- DIY difficulty
- hard
- Estimated cost
- $100 - $1500 (parts and labor)
Network codes mean modules are not communicating. You need a scanner that reads all systems to find the problem.
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Common Symptoms
- Check Engine Light illuminated
- Multiple warning lights on dashboard
- Engine may stall or not start
- Transmission may enter limp mode
- No data on scan tool from ECM
Probable Causes (Ranked by Likelihood)
- ECM power supply or ground failure Very High
- CAN bus wiring fault between ECM and other modules High
- Failed ECM Moderate
- Corroded ECM connector Moderate
Step-by-Step Diagnostic Procedure
-
Check ECM power and ground circuits -- verify battery voltage at ECM connector
-
Inspect ECM connector for corrosion or water damage
-
Check CAN bus wiring from ECM to the gateway module
-
Verify other modules can communicate -- if all are down, suspect CAN bus
-
If ECM has power and ground but does not communicate, ECM replacement may be needed
Common Fixes by Vehicle
What techs usually find when diagnosing U0100 on specific vehicles — tap your vehicle for the fix and the exact part:
2007-2018 Chevrolet Silverado/GMC Sierra moderate DIY
Lost communication with ECM/PCM is a common GM code. Check the PCM power supply fuses first (usually 2 fuses in the underhood fuse box). If fuses are good, check the PCM ground connections at the engine block and firewall. A corroded engine ground strap will cause intermittent U0100. If power and grounds are verified, check for CAN bus wiring damage between the PCM and the OBD port.
Labor: 30 min - 2 hours2008-2020 Ford F-150/Escape/Explorer moderate DIY
On Ford vehicles, U0100 often appears alongside a no-start condition. The PCM is not communicating on the CAN bus. Check the PCM fuse first (usually in the battery junction box). If the fuse is good, the problem is often water intrusion at the PCM connector -- Ford PCMs are located in areas susceptible to water damage. Inspect the PCM connector for corrosion. Use FORScan to attempt communication.
Labor: 1-3 hours2007-2019 Toyota Camry/Corolla/RAV4 moderate DIY
U0100 on Toyota is less common than on domestics and usually indicates a more serious fault. Check battery voltage first -- Toyota CAN bus is very sensitive to low voltage. If the battery is good, inspect the ECM connectors at the firewall. On 2007-2011 Camry, there is a known issue with the ECM connector pins backing out of the housing, causing intermittent communication loss.
Labor: 1-3 hours2008-2020 Chrysler 300/Dodge Charger/Challenger moderate DIY
Chrysler U0100 is frequently caused by the TIPM or a corroded battery cable. The positive battery cable on these vehicles has an integrated fuse block (Intelligent Battery Sensor) that corrodes internally. Check voltage at the PCM fuse with the key on -- if it is below 11.5V, the battery cable needs replacement. Chrysler TSB 08-001-14 covers this.
Labor: 1-2 hoursFrequently Asked Questions
Can I drive with code U0100?
Do not drive. Lost communication codes indicate a module has stopped communicating on the vehicle network. The affected system is completely inoperative.
What causes U0100?
The most common cause is a failed module or a wiring issue in the CAN bus network. ECM power supply or ground failure is the most likely cause. Power supply, ground, and connector issues should be checked before replacing any module.
Is U0100 expensive to fix?
Repair costs range from $100 - $1500 (parts and labor). Wiring repairs are on the lower end, while module replacement is on the higher end. The module may also need to be programmed after replacement.
Sources
This page is built from documented references. Verify against your own service info before repair work.
U0100 on Diesel, EV & Equipment
The same code ID appears across other engines and platforms. The diagnostic flow varies by manufacturer — these are the platform-specific breakdowns:
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