DiagAuto AI Blog https://diagautoai.eu/en/blog Understand your car: OBD2 fault codes, symptoms, practical guides and garage budget. en Sun, 25 Oct 2026 08:00:00 +0000 Which warning lights talk to OBD2 and which do not: engine, glow plugs, DPF, ABS, airbag, battery, oil https://diagautoai.eu/en/blog/which-dashboard-warning-lights-obd2-can-read https://diagautoai.eu/en/blog/which-dashboard-warning-lights-obd2-can-read Sun, 25 Oct 2026 08:00:00 +0000 Symptoms Check engine, ABS, airbag, oil, battery: which lights an OBD2 adapter can read, which go through another control unit, and which cannot be read at all. How many control units does your car let you read? Engine, ABS, airbag, air conditioning https://diagautoai.eu/en/blog/how-many-control-units-obd2-engine-abs-airbag https://diagautoai.eu/en/blog/how-many-control-units-obd2-engine-abs-airbag Sun, 25 Oct 2026 08:00:00 +0000 OBD2 guides An OBD2 adapter reads the engine, but the ABS, airbag or A/C? What the standard requires, what depends on the make and the adapter, and how to find out. Is my car OBD2? Years by country, protocols, and the models that cause problems https://diagautoai.eu/en/blog/is-my-car-obd2-compatible-years-by-country https://diagautoai.eu/en/blog/is-my-car-obd2-compatible-years-by-country Sun, 25 Oct 2026 08:00:00 +0000 OBD2 guides Is your car OBD2? The year it became mandatory in each country, the five protocols, the tricky models and how to check before you buy an OBD2 adapter. Code U0100, lost communication: bad contact, weak battery or failed control unit? https://diagautoai.eu/en/blog/u0100-lost-communication-ecm https://diagautoai.eu/en/blog/u0100-lost-communication-ecm Sun, 25 Oct 2026 08:00:00 +0000 Fault codes Code U0100: a control unit can no longer hear the engine on the CAN network. Battery, earth, connector, added alarm or real failure: the order of the checks. The warning light comes back after clearing: read the freeze frame to catch the fault https://diagautoai.eu/en/blog/check-engine-light-back-after-clearing-freeze-frame https://diagautoai.eu/en/blog/check-engine-light-back-after-clearing-freeze-frame Sun, 25 Oct 2026 08:00:00 +0000 OBD2 guides Check engine light back on after clearing? The freeze frame tells you under what conditions the fault appeared. Two cases explained in detail: P0299 and P0128. O2 sensors P0130 / P0135 / P0141: sensor heater, one of the most common codes after the catalytic converter https://diagautoai.eu/en/blog/p0130-p0135-p0141-o2-sensor-heater https://diagautoai.eu/en/blog/p0130-p0135-p0141-o2-sensor-heater Sun, 25 Oct 2026 08:00:00 +0000 Fault codes Codes P0130, P0135, P0141: dead O2 sensor, failed heater or wiring? How to tell using the live sensor voltage, before you pay for a brand-new O2 sensor. Disconnecting the battery to turn off the warning light: why it does not work and what you lose https://diagautoai.eu/en/blog/disconnect-battery-clear-check-engine-light https://diagautoai.eu/en/blog/disconnect-battery-clear-check-engine-light Sun, 25 Oct 2026 08:00:00 +0000 OBD2 guides Disconnecting the battery often does not clear the check engine light, and when it goes off, the fault remains. Permanent codes, checks reset, settings lost. DPF light on: what standard OBD2 can and cannot see, and when driving is no longer enough https://diagautoai.eu/en/blog/dpf-warning-light-on-what-obd2-sees https://diagautoai.eu/en/blog/dpf-warning-light-on-what-obd2-sees Sun, 25 Oct 2026 08:00:00 +0000 Symptoms DPF light on on a diesel: when a drive on the open road is enough, when you need a garage, and what an OBD2 adapter can or cannot read about the filter itself. Code P0380 / P0670 glow plugs: hard cold starts, what OBD2 tells you https://diagautoai.eu/en/blog/p0380-p0670-glow-plug-codes https://diagautoai.eu/en/blog/p0380-p0670-glow-plug-codes Sun, 25 Oct 2026 08:00:00 +0000 Fault codes Codes P0380, P0670 to P0678 on a diesel: glow plug, glow plug control unit or wiring? The tests to do before replacing all four glow plugs, and the costs. Airbag light on: reading the B code, what can be cleared and what cannot https://diagautoai.eu/en/blog/airbag-light-on-reading-b-code https://diagautoai.eu/en/blog/airbag-light-on-reading-b-code Sun, 25 Oct 2026 08:00:00 +0000 Symptoms Airbag light on: clock spring, connector under a seat, weak battery. What the B code says, what can be cleared, and why you should never touch the module. ELM327 v1.5 or v2.1: the number means nothing, here is how to recognise a good adapter https://diagautoai.eu/en/blog/elm327-v1-5-or-v2-1-good-adapter https://diagautoai.eu/en/blog/elm327-v1-5-or-v2-1-good-adapter Sun, 25 Oct 2026 08:00:00 +0000 OBD2 guides v1.5, v2.1, PIC18F25K80, dual board: what these labels are worth on an ELM327, what the ATZ command returns, and the test to run as soon as it arrives. Code P0128 thermostat: confirm it with the coolant temperature in real time https://diagautoai.eu/en/blog/p0128-thermostat-coolant-temperature-test https://diagautoai.eu/en/blog/p0128-thermostat-coolant-temperature-test Sun, 25 Oct 2026 08:00:00 +0000 Fault codes Code P0128 often blames the thermostat, sometimes the sensor. A simple test: follow the coolant temperature during 10 minutes of driving, then compare it. Code P0335 / P0340, crankshaft and camshaft position sensors: the car stalls or will not start https://diagautoai.eu/en/blog/p0335-p0340-crankshaft-camshaft-sensor https://diagautoai.eu/en/blog/p0335-p0340-crankshaft-camshaft-sensor Sun, 25 Oct 2026 08:00:00 +0000 Fault codes P0335 (crankshaft sensor) or P0340 (camshaft sensor): why the engine stalls or will not start, the rev counter test and the real causes to check, in order. The seller cleared the codes just before your visit: the three signs that show it https://diagautoai.eu/en/blog/used-car-seller-cleared-codes-3-signs https://diagautoai.eu/en/blog/used-car-seller-cleared-codes-3-signs Sun, 25 Oct 2026 08:00:00 +0000 OBD2 guides Light off, no codes: is the car healthy, or was its memory just wiped? Three signs you can read at the OBD2 port, and what the port cannot tell you about it. Pending, confirmed, permanent codes: why your code will not clear https://diagautoai.eu/en/blog/pending-confirmed-permanent-codes-will-not-clear https://diagautoai.eu/en/blog/pending-confirmed-permanent-codes-will-not-clear Sun, 25 Oct 2026 08:00:00 +0000 OBD2 guides You clear the code and it stays or comes back? Pending, confirmed, stored, permanent: what each status means and how to make the code go away for good. Check engine light on but no code found: pending codes, manufacturer codes, control unit not read https://diagautoai.eu/en/blog/check-engine-light-on-no-code-found https://diagautoai.eu/en/blog/check-engine-light-on-no-code-found Sun, 25 Oct 2026 08:00:00 +0000 Symptoms Check engine light on but your OBD2 reader finds no code? Pending or permanent codes, manufacturer codes, another control unit: here is where to look first. Code P0299, turbo underboost: the checks to make before accepting a turbo quote https://diagautoai.eu/en/blog/p0299-turbo-underboost https://diagautoai.eu/en/blog/p0299-turbo-underboost Sun, 25 Oct 2026 08:00:00 +0000 Fault codes Code P0299: the turbo pressure is too low, but the turbo itself is rarely the first culprit. The checks to make in order, before paying for a brand-new turbo. ABS or ESP light on: why a cheap adapter “sees nothing” and how to read C codes https://diagautoai.eu/en/blog/abs-esp-light-on-reading-c-codes https://diagautoai.eu/en/blog/abs-esp-light-on-reading-c-codes Sun, 25 Oct 2026 08:00:00 +0000 Symptoms ABS or ESP light on but “no codes” on your OBD2 reader? Standard OBD2 only reads the engine. Where the C codes are, the likely causes and how serious it is. Clearing the warning light the day before the roadworthiness test: does it show? “Not ready” checks and distance since clearing https://diagautoai.eu/en/blog/clear-codes-before-inspection-readiness-monitors https://diagautoai.eu/en/blog/clear-codes-before-inspection-readiness-monitors Sun, 25 Oct 2026 08:00:00 +0000 OBD2 guides Clearing codes the day before the roadworthiness test leaves three traces in the car: emissions checks not ready, distance since clearing, permanent codes. ELM327 connected via Bluetooth but the car does not respond: 10 causes and fixes on Android https://diagautoai.eu/en/blog/elm327-connected-but-car-not-responding https://diagautoai.eu/en/blog/elm327-connected-but-car-not-responding Sun, 25 Oct 2026 08:00:00 +0000 OBD2 guides Your ELM327 connects to the phone but not to the car? Ignition, protocol, clone, BLE, Android 12 permission: 10 causes to check, one after the other, in order. 7 repairs you can do yourself after an OBD2 diagnosis https://diagautoai.eu/en/blog/7-diy-repairs-after-obd2-diagnosis https://diagautoai.eu/en/blog/7-diy-repairs-after-obd2-diagnosis Thu, 22 Oct 2026 08:00:00 +0000 Garage and budget Fuel cap, air filter, mass airflow sensor, spark plugs, ignition coil, throttle body, glow plugs: 7 simple jobs, no heavy tools, for the most common codes. How to talk to your mechanic when you've already read the fault code https://diagautoai.eu/en/blog/talk-to-your-mechanic-with-fault-code https://diagautoai.eu/en/blog/talk-to-your-mechanic-with-fault-code Thu, 22 Oct 2026 08:00:00 +0000 Garage and budget Arriving at the garage with a fault code, freeze frame data and sensor readings changes the conversation. What to say, what to avoid, how to get a clear quote. How much a garage diagnosis costs, and what an OBD2 app can (or can't) do instead https://diagautoai.eu/en/blog/garage-diagnosis-cost-vs-obd2-app https://diagautoai.eu/en/blog/garage-diagnosis-cost-vs-obd2-app Thu, 22 Oct 2026 08:00:00 +0000 Garage and budget Code reading, full diagnosis, dealer scan tool: typical prices in France, what you get at each price, and where an app like DiagAuto AI is all you need. Code P0087 / P0191: diesel fuel pressure, from the filter to the HP pump https://diagautoai.eu/en/blog/p0087-p0191-diesel-fuel-pressure https://diagautoai.eu/en/blog/p0087-p0191-diesel-fuel-pressure Thu, 22 Oct 2026 08:00:00 +0000 Fault codes P0087 (rail pressure too low) and P0191 (implausible rail pressure sensor) on common rail diesels: fuel filter, HP pump, regulator, injectors. Checks and costs. Buying a used car: scan it with OBD2 before you sign https://diagautoai.eu/en/blog/used-car-obd2-scan-before-buying https://diagautoai.eu/en/blog/used-car-obd2-scan-before-buying Thu, 22 Oct 2026 08:00:00 +0000 OBD2 guides In 10 minutes with an OBD2 adapter, spot fault codes, recently cleared codes or unfinished emissions checks. The pre-purchase scan checklist for a used car. Code P2002 / P2463: diesel particulate filter, regeneration or replacement? https://diagautoai.eu/en/blog/p2002-p2463-diesel-particulate-filter https://diagautoai.eu/en/blog/p2002-p2463-diesel-particulate-filter Thu, 22 Oct 2026 08:00:00 +0000 Fault codes P2002 (DPF efficiency below threshold) and P2463 (soot build-up) on a diesel: short trips, pressure sensor, additive. How to avoid a €1,500 replacement. Roadworthiness test: check your OBD2 codes beforehand to avoid a re-test https://diagautoai.eu/en/blog/check-obd2-codes-before-roadworthiness-test https://diagautoai.eu/en/blog/check-obd2-codes-before-roadworthiness-test Thu, 22 Oct 2026 08:00:00 +0000 OBD2 guides Engine light on means a re-test. 10 minutes with an OBD2 adapter before your appointment can avoid it. What the inspector checks, and the mistakes to avoid. Glow plug light flashing on a diesel: it's not (just) the glow plugs https://diagautoai.eu/en/blog/glow-plug-light-flashing-diesel https://diagautoai.eu/en/blog/glow-plug-light-flashing-diesel Thu, 22 Oct 2026 08:00:00 +0000 Symptoms On most diesels, a glow plug light flashing while driving means an injection or engine management fault, not necessarily the glow plugs. Causes and next steps. Code P0455 / P0442: evaporative system leak, check the fuel cap first https://diagautoai.eu/en/blog/p0455-p0442-evap-system-leak https://diagautoai.eu/en/blog/p0455-p0442-evap-system-leak Thu, 22 Oct 2026 08:00:00 +0000 Fault codes P0455 (large leak) and P0442 (small leak) in the EVAP system: the fuel cap is the number one cause. What to check before you take the car to the garage. Reading your OBD2 sensors in real time: the 10 values to watch https://diagautoai.eu/en/blog/obd2-live-data-10-sensor-values https://diagautoai.eu/en/blog/obd2-live-data-10-sensor-values Thu, 22 Oct 2026 08:00:00 +0000 OBD2 guides Temperature, fuel trims, air flow, intake pressure, O2 sensors… the 10 live readings that tell you more than a fault code, with their normal values explained. White, blue or black exhaust smoke: what it tells you about your engine https://diagautoai.eu/en/blog/white-blue-black-exhaust-smoke https://diagautoai.eu/en/blog/white-blue-black-exhaust-smoke Thu, 22 Oct 2026 08:00:00 +0000 Symptoms Smoke colour is a diagnosis in itself. White: water or coolant. Blue: oil. Black: too much fuel. Causes, how serious it is, and what to check on your car. Code P0101 / P0102: mass air flow sensor, clean it before replacing it https://diagautoai.eu/en/blog/p0101-p0102-mass-air-flow-sensor https://diagautoai.eu/en/blog/p0101-p0102-mass-air-flow-sensor Thu, 22 Oct 2026 08:00:00 +0000 Fault codes P0101 (MAF signal out of range) and P0102 (signal too low): air filter, intake leak, dirty sensor or dead MAF? How to check it, and what it costs. Clearing a fault code: when it helps and when it is a bad idea https://diagautoai.eu/en/blog/clearing-fault-codes-when-it-helps https://diagautoai.eu/en/blog/clearing-fault-codes-when-it-helps Thu, 22 Oct 2026 08:00:00 +0000 OBD2 guides Clearing an OBD2 fault code fixes nothing, but it is a valuable diagnostic tool if done at the right time. What clearing does, what it loses, and when not to. Loss of power uphill: understanding limp mode https://diagautoai.eu/en/blog/loss-of-power-uphill-limp-mode https://diagautoai.eu/en/blog/loss-of-power-uphill-limp-mode Thu, 22 Oct 2026 08:00:00 +0000 Symptoms The car tops out at 2,500 rpm, won't accelerate uphill or on the motorway, then is fine again after a stop. That is limp mode. Common diesel and turbo causes. Code P0401: clogged EGR valve, clean it or replace it? https://diagautoai.eu/en/blog/p0401-egr-valve https://diagautoai.eu/en/blog/p0401-egr-valve Thu, 22 Oct 2026 08:00:00 +0000 Fault codes P0401 (insufficient EGR flow) mostly affects diesels and petrol cars used in town. Symptoms, causes, cleaning, and the cost of replacing the EGR valve. Where is the OBD2 port on my car? Locations by make https://diagautoai.eu/en/blog/where-is-the-obd2-port-by-make https://diagautoai.eu/en/blog/where-is-the-obd2-port-by-make Thu, 22 Oct 2026 08:00:00 +0000 OBD2 guides The OBD2 port is always in the cabin, within a metre of the steering wheel, often behind a cover. Common spots on Peugeot, Renault, VW, BMW, Toyota, Ford… Codes P0300 to P0306: misfires, finding the faulty cylinder https://diagautoai.eu/en/blog/p0300-p0306-misfire-codes https://diagautoai.eu/en/blog/p0300-p0306-misfire-codes Thu, 22 Oct 2026 08:00:00 +0000 Fault codes P0300 = random misfires, P0301 to P0306 = misfire on cylinder 1 to 6. Spark plugs, coils, injector or compression: the simple method to isolate the cause. Rough idle and no fault code: where to start https://diagautoai.eu/en/blog/rough-idle-no-fault-code https://diagautoai.eu/en/blog/rough-idle-no-fault-code Thu, 22 Oct 2026 08:00:00 +0000 Symptoms Unstable idle, shaking engine, yet the OBD2 scanner finds nothing. The causes that never set a code, and how to track them down with live sensor data. Code P0171 / P0174: lean mixture, the 5 causes to check https://diagautoai.eu/en/blog/p0171-p0174-system-too-lean https://diagautoai.eu/en/blog/p0171-p0174-system-too-lean Thu, 22 Oct 2026 08:00:00 +0000 Fault codes P0171 and P0174 signal a lean mixture. Air leak, MAF sensor, injectors, fuel pump: here is the order to search in and how to use the fuel trims to find it. Which OBD2 ELM327 adapter to buy in 2026 (and which to avoid) https://diagautoai.eu/en/blog/which-obd2-elm327-adapter-to-buy https://diagautoai.eu/en/blog/which-obd2-elm327-adapter-to-buy Thu, 22 Oct 2026 08:00:00 +0000 OBD2 guides Bluetooth, BLE or Wi-Fi? An €8 clone or a €40 model? A practical guide to choosing an OBD2 adapter for Android and DiagAuto AI, without bad surprises. Flashing check engine light: why you must stop right away https://diagautoai.eu/en/blog/flashing-check-engine-light-stop https://diagautoai.eu/en/blog/flashing-check-engine-light-stop Thu, 22 Oct 2026 08:00:00 +0000 Symptoms A flashing check engine light is not a simple warning: it signals misfires that can destroy the catalytic converter in a few kilometres. What to do and avoid. Code P0420: catalytic converter at fault, do you really need a new one? https://diagautoai.eu/en/blog/p0420-catalytic-converter https://diagautoai.eu/en/blog/p0420-catalytic-converter Thu, 22 Oct 2026 08:00:00 +0000 Fault codes Code P0420 does not always mean a dead catalytic converter. The real causes, the checks to do before you pay, typical costs and practical advice for drivers. Check engine light on but the car drives fine: is it dangerous? https://diagautoai.eu/en/blog/check-engine-light-on-car-runs-fine https://diagautoai.eu/en/blog/check-engine-light-on-car-runs-fine Thu, 22 Oct 2026 08:00:00 +0000 Symptoms The check engine light is on but everything feels normal. What it monitors, when to worry, and how to find out in 2 minutes what it means with an OBD2 reader.