FAULT CODES · ECU FAMILIES · DIAGNOSTIC ROUTES
Find a starting point for an automotive fault-code or module enquiry. Search the complete code from your scanner, or browse the guides below. Each article explains the information needed before deciding whether a vehicle needs diagnostics, electronic repair or programming.
How to use your diagnostic trouble code
Keep every character, the reporting controller and any suffix or additional information code. Include the vehicle make, model, year and powertrain. Similar-looking codes can have different manufacturer-specific meanings. A stored code describes a detected condition; it does not automatically prove that the named module has failed.
The directory covers selected verified code families. If your code is not listed, send the complete scan for an enquiry. Do not substitute a nearby number or use another model’s repair instructions.
More fault codes, grouped by system
Choose a group to see the code guides. Keep the complete scanner description, including any suffix, when asking about a fault.
Sensor supplies and engine circuits
- P0641, P0642 and P0643: Shared Sensor Supply Faults
- P0670 and P0671-P0674: Glow-Plug Module or Individual Circuit?
- P0571, P0572 and P0573: Brake-Switch Signals and Electrical Warnings
- P0105-P0109: MAP Pressure Readings, Wiring and ECU Inputs
- P0351-P0356: Ignition Coil Circuits and ECU Driver Testing
- P0110-P0114: Intake-Air Temperature Signals After Engine Work
- P0443, P0444 and P0445: EVAP Purge-Valve Electrical Faults
Transmission selectors and lock-up
Body modules and comfort networks
Battery supply and cooling-fan electronics
Browse fault-code guides
P0601 P0602 P0603 P0604 P0605 P0607: ECU Memory and Programming Faults
P0601 · P0602 · P0603 · P0604 · P0605 · P0607 — memory and programming checks.
P0560 P0561 P0562 P0563: Voltage Faults Before ECU Replacement
P0560 · P0561 · P0562 · P0563 · VAG P1602 / 18010 / 005634 — system voltage and supply history.
P0685 P0686 P0687 P0688 P0689 P0690: ECU Power Relay Faults
P0685 · P0686 · P0687 · P0688 · P0689 · P0690 — relay control and monitored supply.
U0001 U0073 U0121 U0140: CAN and Lost Communication Fault Codes
U0001 · U0002 · U0073 · U0100 · U0101 · U0121 · U0122 · U0126 · U0131 · U0140 · U0110 · U0111 — network and module communication.
P0700 P0715 P0716 P0720 P0730: Gearbox Fault Codes Explained
P0700 · P0715 · P0716 · P0720 · P0730 — gearbox control, speed sensing and ratio checks.
P17BF P189C P0841: DSG Pressure and Mechatronic Faults
P17BF · P189C · P0841 — VAG DSG pressure and mechatronic enquiries.
P1570 17978: Immobiliser Start Blocked After ECU Replacement
P1570 / 17978 / 005488 — VAG start-authorisation and replacement-module history.
P0A80 P0A7F P1AC000 P1A8000: Hybrid Battery Warning Codes
P0A80 · P0A7F · P1AC000 · P1A8000 — hybrid battery warning enquiries.
Bosch EDC17 MD1 MG1, Continental SID Simos and Delphi DCM: Identify Your ECU
Bosch EDC17, ME17, MED17, MD1, MG1; Continental SID, Simos, PCR2.1; Delphi DCM and Denso label identification.
Existing diagnostic guides
P0606 processor faults · U0100 and U0101 · BMW FRM lighting faults · Water-damaged electronics
Body, brake, airbag and dashboard modules
For a BCM, BSI, FRM, SAM, ABS/ESP, SRS, instrument cluster or gateway enquiry, include the controller name and complete manufacturer-specific fault text. An engine-only scan may not contain the information needed. We do not assign a universal meaning to every B-code, C-code or manufacturer-specific number.
BCM/BSI · FRM/SAM · ABS/ESP · SRS assessment · Instrument clusters · Network and complex diagnosis
Engine and sensor fault-code guides
Use the exact code and full diagnostic report. These linked guides distinguish the recorded condition from the cause and explain what evidence to send.
P0300, P0301, P0302, P0303, P0304 — misfire
P0335, P0340 — crankshaft and camshaft signals
P0100, P0101 — air-mass measurement
P0115, P0118 — coolant-temperature circuit
P0400, P0401, P0402 — EGR flow
DPF differential-pressure sensor warnings
P2138 — pedal signal correlation
P0130, P0135 — oxygen sensor and heater
P0201, P0202, P0203, P0204 — injector circuits
Body electronics, lighting and mild hybrids
Automatic Wipers or Lights Not Working After a Windscreen Replacement
LED Headlight Module Faults: Water Damage, Identification and Coding
Camera and Radar Warnings After Windscreen, Alignment or Accident Repairs
48-Volt Mild-Hybrid Warnings: Battery, Converter and Starter-Generator Identification
Fuel-pressure codes: P0087, P0088 and P0191
Distinguish a recorded pressure condition from a confirmed ECU failure. Read the fuel-pressure code guide for the code differences and enquiry checklist.
EV charging, battery management and software
EV Charging Faults: AC Charging, DC Charging and On-Board Charger Enquiries · Battery Management Systems: BMS, State of Charge and Battery Health Explained · EV Low-Voltage Warnings: The Battery, DC/DC Converter and Vehicle Electronics · Vehicle Software Updates and OTA: What to Record When a Fault Appears · Zonal Controllers and Vehicle Computers: How Car Electronics Are Changing
Dashboard, ABS, key signals and hybrid isolation
Tyre-pressure warnings and sensor learning
ABS sensors, pump supplies and steering setup
ECU and TCU testing, coding and programming
- P2711: DSG gear disengagement and TCU assessment
- P1740 / P0716: DSG temperature, speed signals and wiring
- P1746: TCU power relay and supply checks
- P1647: ECU coding after replacement
- ECU output testing: voltage and current waveforms
- J2534 programming: preparation for garages
- Intermittent ECU wake-up and fuse-current testing
EV and hybrid case reviews and garage referrals
Engine signals, transmission ratios and coolant-pump circuits
EV charging, hybrid start authorisation and advanced diagnostics
Engine temperature, throttle, timing and starting circuits
- P0116: coolant-temperature plausibility
- P0121: throttle-position plausibility
- P0135: oxygen-sensor heating circuit
- P0325: knock-sensor wiring and mounting
- P0230: fuel-pump primary circuit
- P0650: engine warning-lamp control
- P0016: camshaft and crankshaft correlation
- P0615: starter-relay and no-crank enquiries
Transmission temperature, solenoid and clutch-control codes
High-voltage interlocks, converter signals and 48-volt systems
What if no code is stored?
Describe the symptom and when it happens: no start, intermittent cutting out, missing drive, warning lights, non-working lights or a controller that will not communicate. Keep the original module and note battery, wiring or programming work. The repair finder in our main library can help select an enquiry route.
Send AXION your diagnostic details
For a Didcot workshop enquiry or a suitable UK postal module assessment, send the vehicle model, year, engine or gearbox, full module label, complete scan report and a description of what happened. Include previous battery work, programming, water ingress or replacement parts. Please agree suitability before removing or posting a unit.