Is it safe to keep driving?
Depends on which lights. Airbag and ABS warnings mean those systems may not operate in a crash or an emergency stop, so drive accordingly and get it inspected promptly. Intermittent total electrical dropouts while driving should stop the journey — a vehicle that can lose power steering or lighting unpredictably is not safe in traffic.
General guidance, not a diagnosis of your specific vehicle. If you are unsure, do not drive it and have it inspected.
Battery and charging first, always
Low or unstable system voltage makes control modules behave unpredictably, and many will store communication and implausibility faults when voltage dips. A battery with a failing cell, a corroded terminal, or an alternator with a failed diode will produce a constellation of unrelated-looking warnings. Check voltage at rest and while running before reading anything into the individual codes.
Grounds and connectors
Every module needs a clean ground reference. A corroded chassis ground strap raises the reference voltage for everything sharing it, and sensor readings across several systems drift together. Corrosion from water ingress into a connector or a loom passing through a bulkhead does the same thing locally.
The communication bus
Modern vehicles share a small number of wires between many modules. A single shorted or open wire, or one module failing in a way that floods the bus, takes communication down for everything on it. The symptom is lost-communication codes stored across several modules at once, naming each other — which looks like mass failure but is one wire or one module.
Reading the pattern, not the list
Note which modules report losing contact with which. If three modules all report losing the same one, suspect that module or its supply. If one module reports losing everything, suspect its own connection to the bus. The map of who-cannot-see-whom locates the fault faster than working through codes individually.
What to watch in live data
These are the readings that separate the likely causes. OBDAssistant streams them from an ELM327 adapter while the engine is running, which is what turns a list of possibilities into a diagnosis.
| Reading | What it tells you |
|---|---|
| System voltage, at rest and running | The single most informative reading when multiple systems misbehave. |
| Lost-communication codes across modules | Their pattern locates the break in the network. |
| Module presence on scan | A module the tool cannot reach at all is a stronger clue than any code it might have stored. |
| Freeze-frame voltage | Captures what the supply was doing at the moment the fault was recorded. |
Trouble codes that match this symptom
If the car has already been scanned, these are the codes most often behind it. Each page covers the definition, likely causes, diagnostic steps and repair information.
- U0100 Lost Communication With ECM/PCM "A"
- U0101 Lost Communication with Transmission Control Module (TCM)
- P0562 System Voltage Low
- P0601 Internal Control Module Memory Check Sum Error
- P0606 ECM/PCM Processor Fault
- P0700 Transmission Control System (MIL Request)
Background reading
Questions
Everything went back to normal after I restarted. Is it fine?
No. Intermittent electrical faults are the ones that strand people, and the stored codes from the episode are the best evidence you will have. Scan it while the codes are still there rather than waiting for it to happen again.
Could a cheap scan adapter cause this?
A poor-quality adapter left permanently plugged into the diagnostic socket can keep the bus awake, drain the battery and, in bad cases, interfere with communication. If the symptoms started after fitting one, unplug it and retest before anything else.
Is it worth clearing the codes to see which come back?
Only after recording them all first. The pattern across modules is the diagnosis, and once cleared you cannot get it back without reproducing the fault.