OBD2 advice centre
OBD2 guides: fault codes, warning lights and diagnostics
Find an answer to your question and practical steps for using your OBD2 reader.
27 practical guidesCar Scanner iPhone / Android
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The answers drivers genuinely need.
Each guide separates what OBD2 can confirm, what it can only suggest and when professional help is appropriate.
01
Installation · 6 min
Where is the OBD2 port in your car?
Find the 16-pin OBD2 diagnostic port without unnecessary dismantling and connect OBDPhone® safely.
Read the article →16OBD2
02
Diagnostics · 8 min
Check-engine light: understanding an OBD2 fault code
Understand an OBD2 engine code, save the useful evidence and choose the next step without guessing which part to replace.Read the article →03Understanding · 7 min
OBD2 or manufacturer diagnostic tool: what is the difference?
Compare generic OBD2 diagnostics with manufacturer tools for engine codes, ABS, airbags, coding and workshop functions.Read the article →04Compatibility · 9 min
OBD2 compatibility: petrol, diesel, hybrid or electric
Understand how model year and fuel type affect OBD2 compatibility before connecting OBDPhone®.Read the article →05Good practice · 7 min
Clearing an OBD2 fault code: when and how
Learn what fault-code clearing does, what evidence to save and why the warning light may return.Read the article →06Fault codes · 10 min
P0401 fault code: EGR valve, carbon build-up or another cause?
P0401 means that EGR flow was judged insufficient. Learn the possible causes, useful checks and why the EGR valve is not always at fault.Read the article →07Fault codes · 11 min
P2002 fault code: blocked, damaged DPF or another cause?
P2002 indicates DPF efficiency below threshold. Learn the causes, the difference from P2463/P242F and the limits of regeneration.Read the article →08Fault codes · 11 min
P0101 fault code: MAF sensor, air leak or another cause?
P0101 does not automatically condemn the MAF sensor. Review causes, sensible checks and five documented manufacturer cases.Read the article →09Fault codes · 12 min
P0016 fault code: timing chain, sensor or correlation?
P0016 reports an implausible crankshaft–camshaft correlation. Understand urgency, checks and five verified manufacturer cases.Read the article →010Fault codes · 11 min
P0128 fault code: thermostat, sensor or engine temperature?
P0128 reports slower or lower coolant warm-up than expected. Causes, safe checks and five verified manufacturer cases.Read the article →011Fault codes · 12 min
P0456 fault code: fuel cap, small EVAP leak or another cause?
P0456 reports a very small EVAP leak without proving the fuel cap has failed. Safe checks and six verified manufacturer cases.Read the article →012Fault codes · 12 min
P0340 fault code: camshaft sensor, wiring or another cause?
P0340 reports a camshaft-position sensor circuit issue without proving the sensor has failed. Checks and verified manufacturer cases.Read the article →013Fault codes · 12 min
P0201 fault code: injector 1, wiring or another cause?
P0201 reports a cylinder 1 injector-circuit fault without proving the injector has failed. Checks and verified manufacturer cases.Read the article →014Diagnostics · 8 min
Permanent fault code will not clear: what to do after a repair
A permanent OBD2 code remains after repair? Learn why clearing is not enough, what evidence to keep and when to return to the workshop.Read the article →015Fault codes · 11 min
P0441 fault code: EVAP purge valve, hose or another cause?
P0441 reports incorrect EVAP purge flow without automatically proving the valve has failed. Safe checks and five verified manufacturer cases.Read the article →016Practical diagnostics · 8 min
OBD2 freeze frame: what should you save before clearing a code?
Understand OBD2 freeze-frame data, separate it from live readings and prepare useful information for your garage before clearing codes after repair.Read the article →017Maintenance and prevention · 7 min
Engine oil above the maximum mark: can you drive?
Oil above MAX after topping up or a service? Check the reading, avoid a risky restart and prepare the right information for your garage.Read the article →018Maintenance and diagnosis · 8 min
Coolant level keeps dropping: what to check before topping up
Coolant dropping with no puddle beneath the car? Assess the urgency, record useful observations and understand what an OBD2 scan can and cannot tell you.Read the article →019Fault codes · 9 min
P0135 fault code: oxygen sensor, wiring or power supply?
P0135 points to the upstream oxygen sensor heater circuit. See what to save and why a documented wiring issue does not justify replacing every sensor.Read the article →020Fault codes · 9 min
P0113 fault code: intake-air sensor or wiring?
P0113 reports a high signal in the intake-air temperature sensor circuit. Learn what to save and check before ordering a sensor.Read the article →021Fault codes · 8 min
P0011 code: oil control, cam timing or recent repair?
P0011 concerns intake camshaft timing performance. Save the right clues before replacing a solenoid or erasing the code.Read the article →022Fault codes · 8 min
P0174 fault code: lean mixture on bank 2, what next?
P0174 flags a lean mixture correction on bank 2. Compare related codes and three manufacturer cases before buying parts.Read the article →023Fault codes · 8 min
P0087 fault code: fuel pressure too low, what should you do?
P0087 reports insufficient fuel pressure. Learn what to save, when to stop and why one official GM case does not justify replacing the pump.Read the article →024Fault codes · 9 min
P0301 fault code: cylinder 1 misfire, what should you check?
P0301 reports a cylinder 1 misfire. Symptoms, urgency and three manufacturer cases before replacing a plug, coil or injector.Read the article →025Fault codes · 9 min
P0234 fault code: turbo boost too high, what should you check?
P0234 reports excessive boost. Urgency, data to save and three manufacturer cases before replacing the turbocharger.Read the article →026Fault codes · 9 min
P0562 fault code: what should you check when system voltage is low?
P0562 reports low electrical-system voltage. Battery, cables, grounds, charging and three manufacturer cases before replacing parts.Read the article →027Practical diagnostics · 7 min
Engine light on but no OBD2 codes: what should you check?
Engine warning light on but your OBD2 reader finds no faults? Check the warning, connection and scan coverage before drawing conclusions or clearing anything.Read the article →Editorial principles
Clear about what OBD2 can — and cannot — do.
We focus on useful, cautious guidance: no random parts replacement and no compatibility claim without context.
Every guide links back to the OBDPhone® checker so general information leads to a vehicle-specific answer.