#OBD-II
35 posts in Car Diagnostics blog about "OBD-II" — OBD-II diagnostics, DTC codes, repair. ← All posts
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Variable displacement AC compressor: why "new refrigerant" doesn't help, and how OBD sees a sick pump
Fixed vs variable displacement AC compressor, how to diagnose the control valve, code B1247, symptoms, and why "clutch not engaging" isn't always an electric fault.
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Ford EcoBoost 1.5 / 2.0: typical OBD codes every Ford mechanic knows
Ford EcoBoost turbocharged specifics: P0299 turbo, P0301 misfire, P0016 timing chain, P0087 fuel pressure — real problem statistics for this engine family.
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The 8 AI agents behind Car Diagnostics: how a specialized AI team explains your car fault
What each of the 8 Car Diagnostics AI agents does: DTC Analyzer, Prediction, Recommendation, Report Generator, Chat, OBD Reader, RAG and Diagnostic MCP. How they work together — and why that's more accurate than a single big ChatGPT.
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ABS wheel speed sensor: codes C0035, C0040, C0045 and how to diagnose "ABS flashing in turns"
What OBD-II shows about wheel speed sensors, difference between active and passive types, how to diagnose ABS/ESP problems via C-codes, and why a "worn tone ring" is common.
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ADAS: when Lane Keep and Adaptive Cruise stop working, and why OBD calibration isn't "out of the box"
Lane Keep Assist, Adaptive Cruise Control, AEB via OBD-II: typical codes U0428, C1B01, why calibration is needed after windshield replacement, and why an OBD adapter won't do it.
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ABS bleeding via scan tool: why "the normal way" won't bleed the air out, and how OBD activates the valves
How to bleed brakes with ABS: activate the ABS pump via OBD scanner, why air stays in the module manually, which cars support self-bleed.
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AC not cooling: OBD-II diagnostics, refrigerant pressure, compressor and sensors
What OBD-II shows about the AC system: codes B1234, B10DA, high/low-side pressure, evaporator temperature, why "just add refrigerant" isn't always the answer, and how to diagnose the compressor clutch.
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Auto Start-Stop not working: 8 reasons the system won't kill the engine at traffic lights
Why Auto Start-Stop suddenly stopped working, how OBD-II shows the status (Ready/Not Ready), ECU criteria for the stop, the role of the EFB/AGM battery, and how to diagnose via live parameters.
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Battery and alternator via OBD-II: P0562, P0620, diagnose in 5 minutes
What OBD-II says about the battery and alternator: codes P0562 (low voltage), P0563 (high), P0620 (alternator). How to read system voltage and why "overcharge" is more dangerous than "undercharge".
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BCM (Body Control Module): diagnosing "window won't work" and "key not detected" via OBD
What BCM does, how OBD-II reads B-codes and U-codes, why "the window is stuck from pause" is often the BCM, and how to tell the module from a wiring fault.
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Brake pad wear via OBD-II: how BMW, Audi, Mercedes "count" remaining life
What OBD-II shows about brake pads on modern cars: wear sensors, calculated brake pad wear, codes C1000, C1100, and why "2000 mi to replacement" on a BMW is not guesswork.
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CAN-FD (Flexible Data-Rate): why new cars "don't talk" to your old ELM327
What CAN-FD (Bosch, 2012) is, how it differs from classic CAN, why Tesla, Ford Bronco, BMW 2020+ need new OBD adapters, and how to check if your ELM327 supports CAN-FD.
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Car won't start: how OBD-II tells an immobilizer fault from fuel/electrical
Step-by-step algorithm for "no-start": how OBD-II tells in 5 minutes whether the issue is the immobilizer (P1602, B10CC), fuel pump, starter, battery or ECU.
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OBD-II on Chinese cars: Chery, Geely, BYD, Great Wall — diagnostic specifics
What OBD-II can do on Chery Tiggo, Geely Coolray, BYD Tang, Great Wall Haval: SAE J1979 standard, custom PIDs, GB codes, brand tools vs universal ELM327.
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DPF (Diesel Particulate Filter): diagnosing regeneration, clogging and when it's time for a clean
What a DPF is, how it regenerates, which DTCs signal a problem (P2002, P244A, P244B), how to read soot levels via OBD-II, and why short trips kill diesel engines.
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Not all DTCs are equal: 4 severity levels (low, medium, high, critical) and how to prioritize
What DTC severity level means, how to tell "light from dust on the MAF" from "stop the engine now", which codes can wait, which are critical right now.
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Engine oil pressure via OBD-II: codes P0521, P0524, why it's "shut down now" and how to diagnose
What OBD-II shows when oil pressure drops: P0520-P0524, difference between "high" and "low", when you can't drive another meter, worn pump, clogged filter or worn bearings.
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EV and hybrid OBD-II diagnostics: Tesla, Nissan Leaf, hybrids, and where the standard ends
What OBD-II can and can't do on electric vehicles: hybrid diagnostics for Toyota Prius, reading battery health on Nissan Leaf, Tesla's limitations, and the role of manufacturer CAN.
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Odometer fraud: how OBD-II reveals rolled-back mileage when buying used
What OBD-II shows when the odometer says 50 000 mi but the real number is 150 000: ECU log audit, mismatch between ABS, ECM and cluster, motohours vs mileage, DTC history analysis.
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How to reset service intervals via OBD-II — and why sometimes it's impossible
Step-by-step guide to reset the "Service in 500 mi" reminder on VW, BMW, Mercedes, Toyota. Button method vs diagnostic method, when online activation is needed, and why the dealer charges $80 for a 30-second job.
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HVAC deep-dive: climate control via OBD, blend-door actuators, servo motors — when the cabin heats "from one side"
Dual-zone climate control via OBD: codes B12xx, blend-door actuator state, mode-door, vent output temperature. How to diagnose "warm on the right — cold on the left".
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OBD logging for track day: capturing engine data on track and what to do with the log
What to log on track via OBD-II (RPM, boost, oil temp, EGT, coolant), what rate (1 Hz vs 10 Hz), how not to lose data in corners, how to export into RaceRender / Trackaddict.
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Freeze Frame: how OBD "photographs" the moment of a fault and why it matters more than the DTC itself
What OBD-II Freeze Frame data is, which parameters it captures, how to read the ECU snapshot, and why an experienced diagnostician looks at it before the trouble code itself.
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OBD-II Mode 06: reading the ECU's inner thoughts before Check Engine appears
What OBD-II Mode 06 is, how to read on-board monitor test results (catalyst, O2, EGR) before a DTC appears, and why it's a secret weapon of professional diagnosticians.
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P0128: why the engine won't warm up — thermostat, sensor or something sneakier
Deep dive into P0128: when it appears, why thermostats fail stuck open, how to diagnose without teardown, and why a "cold" engine burns 10-15% more fuel.
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Post-repair verification: 7 OBD steps to confirm the fix actually worked
What to do after replacing an O2 sensor, catalyst, MAF or injector: run a drive cycle, read Freeze Frame, Mode 06, compare LTFT before/after — to be sure the repair is solid.
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TPMS via OBD-II: why the "yellow circle" turned on and how to diagnose tire-pressure sensors
Direct vs indirect TPMS, codes C0750, C0755, C2126, how to read individual pressure and temperature per wheel via OBD-II, sensor battery life, replacement cost.
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UDS Mode 22: what manufacturers hide beyond the OBD-II standard
What UDS (Unified Diagnostic Services) ISO 14229 is, difference vs OBD-II, how Mode 22 reads DPF soot mass, VGT position, TPMS voltage — and why 90% of the "interesting stuff" lives here.
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Engine Stalls While Driving: 10 Causes and Urgent Diagnosis
Engine suddenly dies while driving — under braking, at lights, on the motorway: how to find the cause in 15 minutes and whether you can keep driving.
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OBD-II Readiness Monitors explained: why they matter before an MOT or Smog Check
What OBD-II Readiness Monitors are, why cars fail inspection with "not ready" status even without any trouble codes, and how to run a proper drive cycle after battery disconnect or repair.
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Car Will Not Start: 12 Causes and a Quick Diagnostic Algorithm
Engine cranks but no fire — or dead silence: how to tell in 5 minutes whether it is the starter, the battery, fuel, plugs, immobiliser, or something deeper.
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How AI Explains Trouble Codes: 8 Agents Under the Hood
How Car Diagnostics AI works: eight specialised agents analyse DTC codes, predict failures, generate reports, and answer questions — inside a microservice architecture.
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Car Battery Warning Lights: What the Dashboard Battery Symbol Means
Complete guide to car battery and charging system warning lights: what the red battery symbol means, the difference between red and amber indicators, and how to diagnose charging faults before they leave you stranded.
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5 OBD-II Protocols Explained in Plain English
ISO 9141-2, KWP2000, J1850 PWM, J1850 VPW, CAN — how they work, which cars use them, and why protocol support matters when choosing an adapter.
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P0420: Why the Catalytic Converter "Fails"
A detailed breakdown of code P0420: what "catalyst efficiency below threshold" means, common causes, how to diagnose it, repair costs, and whether you can keep driving.