AI-powered OBD-II fault code diagnostic tool for UK drivers

OBD2 Fault Code Library

Browse the full AI-Diagnostics-Pro fault code library. Every link below points to a crawlable code page with UK repair-cost context, MOT relevance, and next-step guidance.

Start with the exact code from your scanner, then follow the related-code links on each page if you need to compare similar faults or spot patterns that often appear together.

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Powertrain codesChassis codesBody codesNetwork codes

Powertrain codes

Engine, emissions, fuel, ignition, turbo, cooling and transmission-related OBD2 fault codes.

P0A0F
Drive Motor A Performance
P0A09
DC/DC Converter Status Circuit Low
P0BBE
Hybrid Battery Voltage System Isolation Fault
P0010
A Camshaft Position Actuator Circuit Bank 1
P0011
A Camshaft Position Timing Over-Advanced Bank 1
P11A0
EGR Cooler Bypass Control Circuit
P0012
A Camshaft Position Timing Over-Retarded Bank 1
P0014
B Camshaft Position Timing Over-Advanced Bank 1
P0016
Timing Correlation Fault — Sensor, Chain or VVT Problem?
P20E8
Reductant Injection Performance
P0087
Low Fuel Pressure — Pump, Filter or Regulator?
P0088
Fuel Rail/System Pressure Too High
P0089
Fuel Pressure Regulator Performance
P0093
Fuel System Leak Detected Large Leak
P0101
MAF Sensor Out of Range — Clean or Replace?
P0102
Mass Air Flow Circuit Low Input
P0103
Mass Air Flow Circuit High Input
P0113
IAT Sensor High Reading — Connector & Wiring Checks
P0115
Engine Coolant Temperature Circuit Malfunction
P0116
Engine Coolant Temperature Circuit Range/Performance
P0117
Engine Coolant Temperature Circuit Low Input
P0118
Engine Coolant Temperature Circuit High Input
P0120
Throttle Position Sensor Circuit Malfunction
P0121
Throttle Position Sensor Circuit Range/Performance
P0128
Thermostat Stuck Open — Engine Won't Warm Up Properly
P0130
O2 Sensor Circuit Malfunction Bank 1 Sensor 1
P0131
O2 Sensor Circuit Low Voltage Bank 1 Sensor 1
P0132
O2 Sensor Circuit High Voltage Bank 1 Sensor 1
P0133
O2 Sensor Circuit Slow Response Bank 1 Sensor 1
P0135
Upstream O2 Sensor Heater Fault — Fuse, Wiring or Sensor?
P0136
O2 Sensor Circuit Malfunction Bank 1 Sensor 2
P0137
O2 Sensor Circuit Low Voltage Bank 1 Sensor 2
P0138
O2 Sensor Circuit High Voltage Bank 1 Sensor 2
P0141
Downstream O2 Sensor Heater Fault — Underbody Wiring Check
P0150
O2 Sensor Circuit Malfunction Bank 2 Sensor 1
P0155
O2 Sensor Heater Circuit Malfunction Bank 2 Sensor 1
P0161
O2 Sensor Heater Circuit Malfunction Bank 2 Sensor 2
P0171
System Too Lean — Vacuum Leak or Fuel Delivery Problem?
P0172
System Too Rich Bank 1
P0174
Bank 2 Lean Condition — MAF, Intake or Fuel Injector Fault?
P0175
System Too Rich Bank 2
P0190
Fuel Rail Pressure Sensor Circuit Malfunction
P0191
Fuel Rail Pressure Out of Range — Sensor or Pump Fault?
P203F
Reductant Level Sensor Performance
P0217
Engine Overtemp Condition
P0234
Turbo Overboost — Wastegate, Actuator or Vacuum Fault?
P0235
Boost Sensor Circuit Fault — Wiring & Live Data Checks
P0236
Boost Sensor Range Fault — Requested vs Actual Boost
P0299
Turbo Underboost — Boost Leak, Wastegate or Failing Turbo?
P0300
Multi-Cylinder Misfire — Why It Happens & How to Fix It
P0301
Cylinder 1 Misfire Detected
P0302
Cylinder 2 Misfire Detected
P0303
Cylinder 3 Misfire Detected
P0304
Cylinder 4 Misfire Detected
P0305
Cylinder 5 Misfire Detected
P0306
Cylinder 6 Misfire Detected
P0316
Misfire Detected on Startup First 1000 Revolutions
P0335
Crankshaft Position Sensor A Circuit Malfunction
P0336
Crankshaft Position Sensor A Circuit Range/Performance
P0340
Cam Sensor Fault — Wiring, Timing or Sensor Failure?
P0341
Camshaft Position Sensor Circuit Range/Performance Bank 1
P0345
Camshaft Position Sensor A Circuit Bank 2
P0351
Ignition Coil A Primary/Secondary Circuit Malfunction
P0352
Ignition Coil B Primary/Secondary Circuit Malfunction
P0353
Ignition Coil C Primary/Secondary Circuit Malfunction
P0354
Ignition Coil D Primary/Secondary Circuit Malfunction
P0400
Exhaust Gas Recirculation Flow Malfunction
P0401
EGR Flow Insufficient — Carbon Buildup or Valve Fault?
P0402
Exhaust Gas Recirculation Flow Excessive Detected
P0403
Exhaust Gas Recirculation Circuit Malfunction
P0411
Secondary Air Injection System Incorrect Flow Detected
P0420
Cat Efficiency Below Threshold — Check O2 Sensors Before Replacing
P0421
Warm-Up Cat Efficiency Fault — Cold-Start Catalyst Problem
P0430
Bank 2 Cat Efficiency Fault — Causes, Costs & First Checks
P0431
Warm Up Catalyst Efficiency Below Threshold Bank 2
P0440
Evaporative Emission Control System Malfunction
P0442
Small EVAP Leak — Fuel Cap, Hose or Purge Valve?
P0446
EVAP Vent Control Fault — Vent Valve & Canister Checks
P0455
Large EVAP Leak — Often Just a Loose Fuel Cap
P0456
Very Small EVAP Leak — Sealing & Hose Checks
P0457
EVAP Leak From Fuel Cap — Cheapest OBD2 Fix Available
P0480
Cooling Fan 1 Control Circuit Malfunction
P0505
Idle Control System Malfunction
P0506
Idle Control System RPM Lower Than Expected
P0507
Idle Control System RPM Higher Than Expected
P0520
Engine Oil Pressure Sensor/Switch Circuit Malfunction
P0521
Engine Oil Pressure Sensor/Switch Range/Performance
P0522
Engine Oil Pressure Sensor/Switch Low Voltage
P0562
System Voltage Low
P0563
System Voltage High
P0700
Transmission Control System Malfunction
P0715
Input/Turbine Speed Sensor Circuit Malfunction
P0720
Output Speed Sensor Circuit Malfunction
P0730
Incorrect Gear Ratio
P0741
Torque Converter Clutch Circuit Performance or Stuck Off
P0750
Shift Solenoid A Malfunction
P0755
Shift Solenoid B Malfunction
P1610
NATS Malfunction Immobiliser Fault
P2002
Diesel Particulate Filter Efficiency Below Threshold Bank 1
P2003
Diesel Particulate Filter Restriction Ash Accumulation Bank 1
P2200
NOx Sensor Circuit Bank 1
P2201
NOx Sensor Circuit Range/Performance Bank 1
P2459
Diesel Particulate Filter Regeneration Frequency

Chassis codes

ABS, wheel-speed, traction-control and other chassis or braking-system related codes.

C0035
Left Front Wheel Speed Sensor Circuit
C0040
Right Front Wheel Speed Sensor Circuit
C0045
Left Rear Wheel Speed Sensor Circuit
C0050
Right Rear Wheel Speed Sensor Circuit
C0300
Rear Propshaft Speed Sensor Circuit Malfunction
C0750
Tyre Pressure Monitoring System Sensor Fault

Body codes

Airbag, restraint-system and body-electronics fault codes.

B0001
Driver Frontal Stage 1 Deployment Control
B0051
Passenger Frontal Stage 1 Deployment Control

Network codes

Communication and control-module network fault codes.

U0100
Lost Communication With ECM PCM
U0121
Lost Communication With ABS Control Module
U0140
Lost Communication With Body Control Module
U0401
Invalid Data Received From ECM PCM