U0100: Lost Communication With ECM/PCM A
What Does U0100 Mean?
U0100 is a diagnostic trouble code indicating: Lost Communication With ECM/PCM A. This code relates to the network communication system. It has been reported in NHTSA complaints across 23 different vehicle models.
Symptoms of U0100
- ⚠️ Check engine light illuminated
- ⚠️ Poor fuel economy
- ⚠️ Engine misfires
- ⚠️ Loss of engine power
- ⚠️ Vehicle won't start
- ⚠️ Jerking or surging while driving
Common Causes
- 🔍 Worn or fouled spark plugs
- 🔍 Weak or failing fuel pump
- 🔍 Clogged or leaking fuel injector
- 🔍 Dirty or failed MAF sensor
- 🔍 Failed PCV valve
- 🔍 Wiring or connector problem
U0100 Reports by Year
Real Owner Reports
From NHTSA complaint database — actual owner descriptions.
"3 TIMES OVER THE LAST MONTH, WHILE I WAS DRIVING MY VEHICLE, THE CAR SUDDENLY LOST POWER WHILE I WAS DRIVING ON THE HIGHWAY. ALL THE DASHBOARD LIGHTS FLASHED ON, CHECK ENGINE LIGHT AND WARNING LIGHTS ILLUMINATED. THE VEHICLE LOST POWER, THE ACCELERATOR WAS NOT WORKING, AND I WAS JUST BARELY ABLE TO "
— Toyota Highlander owner, 11/03/2020
"DRIVING ON SB HWY 35 AT 74MPH, MASTER WARNING LIGHT CAME ON AND VEHICLE SHUT DOWN, NO ELECTRICAL OR ENGINE CONTROL. PULLED SAFELY TO SHOULDER OF ROAD. CAR WOULD NOT RESTART. GOT OUT OF CAR, LOCKED CAR, UNLOCKED CAR (TOYOTA TECHNICIAN INSTRUCTIONS), THEN CAR RESTARTED. GOT CAR OFF THE ROAD, CONTA"
— Toyota Prius owner, 10/14/2014
"Our battery died in April 2025. We've had this car since October 2021 with only 8 miles on it. We've replaced: The PCV valve The PCV valve tube The MAF sensor The sparks plugs 3 times which was $90 each time Replaced our battery 2 times since April 2025 3 oil changes And finally replacing our ent"
— Honda Civic owner, 04/07/2025
Source: NHTSA Complaints Database
Most Reported Vehicles for U0100
Based on NHTSA owner complaint data.
| # | Vehicle | Reports |
|---|---|---|
| 1 | DODGE CHARGER | |
| 2 | CHEVROLET EQUINOX | |
| 3 | FORD FOCUS | |
| 4 | DODGE DURANGO | |
| 5 | CHRYSLER 300 | |
| 6 | TOYOTA PRIUS | |
| 7 | CHEVROLET SILVERADO | |
| 8 | CHEVROLET MALIBU | |
| 9 | CHEVROLET TAHOE | |
| 10 | TOYOTA HIGHLANDER | |
| 11 | HONDA CIVIC | |
| 12 | HONDA ACCORD | |
| 13 | HONDA INSIGHT | |
| 14 | FORD EXPLORER | |
| 15 | FORD FUSION |
U0100 Reports by Vehicle
Detailed NHTSA complaint analysis for each vehicle model.
Diagnostic Tips
- Scan all modules, save freeze-frame data, and clear unrelated history codes before focusing on U0100.
- Confirm whether companion codes are present first; they often identify the root cause sooner than the headline DTC.
- Prioritize inspection around electrical system and the most common failure path for this code family.
- Perform a voltage-drop and continuity check on the affected circuit and verify 5V reference/ground stability under load.
- After each repair step, complete one drive cycle and verify readiness monitors instead of judging success after a quick idle test.
- If the code keeps returning on high-incidence platforms (for example DODGE CHARGER), check TSB patterns and wiring/connector fitment before major part replacement.
Common Mistakes to Avoid
- ❌ Skipping freeze-frame review and losing the exact RPM/load conditions when the fault set.
- ❌ Replacing modules before checking grounds, voltage drop, and harness rub-through near heat/vibration points.
- ❌ Clearing U0100 and returning the car before monitors complete — this often creates repeat visits.
- ❌ Treating intermittent wiring or connector faults as permanent component failure without wiggle testing.
Frequently Asked Questions
What causes communication codes?
Can a bad battery cause network codes?
What To Do Next
Possible Fixes
- 🔧 Have the code scanned with a professional-grade scanner to read freeze frame data
- 🔧 Test the relevant sensor(s) with a multimeter before replacing
- 🔧 Inspect wiring harness and connectors for damage, corrosion, or loose connections
- 🔧 Check battery voltage and ground connections; inspect CAN bus wiring
- 🔧 If DIY repair isn't feasible, get a diagnostic from a trusted mechanic ($50-150)
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Find your vehicle above
Click your make and model for real owner reports and common causes specific to your vehicle.
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Check for recalls
Go to nhtsa.gov/recalls and enter your VIN. Free repairs if covered.
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Get a professional diagnosis
A code alone doesn't identify the exact failed part. A diagnostic ($50–$150) pinpoints the root cause.