U0100: Lost communication with ECM/PCM A
What the code tells you on its own
- System
- Network
- Functional group
- Bus communication
- Failure type byte, when the tool sends one
- 20 (Signal invalid)
Communication faults — a module that stopped answering on the CAN bus, or sent implausible data. Often a symptom of a power or wiring problem rather than a failed module.
Scan tools report the same fault as U0100 and as U0100xx, where xx is a sub-type. They are one fault, and whether the sub-type appears at all depends on the tool and the protocol rather than on the car.
What we see when U0100 turns up
Measured across the diagnostics run through Wrenchlane, not taken from a reference table. Figures as of 2026-10-06.
- Diagnostics
- 11
- Separate workshops
- 9
- Arrived code only
- 18%
- Most common marque
- Nissan
May 2026 to September 2026
Not one shop meeting it repeatedly
No symptom description entered at all
Where we have seen it most
These are counts from our own work, not a claim about how common the fault is across all vehicles. They describe what independent workshops brought to us, which is a narrower and more specific thing.
What U0100 usually turns up with
Measured across our own diagnostics. The multiplier is how much more often the two appear together than chance would predict, so a high number means the pair is telling you something a single code is not. Codes rarely arrive alone, and reading the set is usually faster than chasing the first one on the list.
| Code | What it is | Seen together | Versus chance |
|---|---|---|---|
| B2193 | Not individually documented | 3 times | 174.6x |
| B24A9 | Not individually documented | 3 times | 174.6x |
| B260F | Not individually documented | 3 times | 174.6x |
| C1199 | Manufacturer-specific, meaning depends on the marque | 3 times | 174.6x |
| U1000 | Manufacturer-specific, meaning depends on the marque | 3 times | 131x |
Run U0100 against the car in front of you
Enter the code and the symptoms and get ranked probable causes for that specific vehicle, with the checks in the order worth doing them. Free account, no card.
Start freeOther bus communication codes
- U0416 Invalid data received from vehicle dynamics control module
- U0401 Invalid data received from ECM/PCM A
- U0121 Lost communication with ABS control module
- U0167 Lost communication with immobiliser control module
- U0155 Lost communication with instrument panel cluster
- U0019 Low speed CAN communication bus
- U0103 Lost communication with gear shift module
- U0102 Lost communication with transfer case control module
FAQ
Frequently asked questions
How do I run a diagnosis?
Select the vehicle on Start, click the Diagnostic card and choose New diagnostic. Fill in the description, the error codes and the mileage, then click Analyze.
Learn more: Diagnostic (vehicle-first start), Diagnostic form: description, error codes and mileage
Do I have to type the codes from my scan tool?
No. Click the camera button next to Error codes and take or choose a photo (JPEG or PNG) of the scan tool's screen; WrenchLane reads the codes and their descriptions into the form. You can also speak them with the microphone.
Learn more: OBD reader photo scan (fault codes from a photo), Voice input for the problem description
Are the public fault code pages built from my diagnostics?
They are built from anonymised, aggregated diagnostics run in WrenchLane; no workshop, customer or vehicle can be identified. Each fault code page shows how often the code was seen across those diagnostics and in how many separate workshops.
Learn more: Fault code pages on wrenchlane.com (fault-code cluster)