Cylinder 1 glow plug circuit. Seen in 3 real diagnostics across 3 workshops.
What the code tells you on its own
- System. Powertrain. Engine, fuel, air, ignition, emissions and transmission. The overwhelming majority of what workshops bring to the AI.
- Functional group. Glow plugs and preheat
- Subsystem. Computer output circuit and ECU
- Failure type byte, when the tool sends one. 00 (No sub-type information). Scan tools report the same fault as P0671 and as P0671xx, where xx is a sub-type. They are one fault, and whether the sub-type appears depends on the tool and the protocol rather than on the car.
What we see when P0671 turns up
Measured across the diagnostics run through Wrenchlane by independent workshops, not taken from a reference table. Sightings span April 2026 to July 2026.
- 3 diagnostics carried this code.
- 3 separate workshops met it, so this is not one shop seeing the same fault repeatedly.
- 33% of the time it arrived with no symptom description at all, meaning the technician had nothing but the code to work from.
- Most often on Volkswagen, which is where we have seen it most rather than a claim about the fleet at large.
What this page does not tell you
A code names a symptom the car noticed, not the part that failed. P0671 on one vehicle and the same code on another can have different causes, and the counts above describe what independent workshops brought to us rather than how common the fault is across all cars. Getting from the code to the cause needs the vehicle: its make, model, engine and what it is actually doing.
Run P0671 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.
Other glow plugs and preheat codes
- P0685, ECM/PCM power relay control circuit open
- P0675, Cylinder 5 glow plug circuit
- P0684, Glow plug control module to PCM communication circuit range/performance
- P0380, Glow plug or heater circuit A
- P0672, Cylinder 2 glow plug circuit
- P0683, Glow plug control module to PCM communication circuit