Diagnostic Codes & Symptoms
Tech-to-tech diagnostic strategy. No customer fluff — just what to check, what to watch on the scan tool, and where the pattern failures hide.
Diagnostic Trouble Codes
P0016: Crankshaft/Camshaft Correlation — Diagnosis and Causes
P0016 crank/cam correlation diagnosis. Timing chains, VVT solenoids, cam phasers, and pattern failures on GM, Ford, Hyundai/Kia.
Timing / Cam-CrankP0011: Intake Cam Timing Over-Advanced — What to Check First
P0011 intake cam timing over-advanced diagnosis. VVT solenoid sludge, cam phasers, timing chains. Pattern failures on GM, Hyundai/Kia, Subaru.
Timing / Cam-CrankP0340: Camshaft Position Sensor Circuit — Diagnosis Guide
P0340 camshaft position sensor circuit diagnosis. CMP sensor scope testing, wiring faults, reluctor damage. Pattern failures on Nissan, Ford, Jeep, GM.
Misfire CodesP0300: Random/Multiple Cylinder Misfire — Diagnostic Strategy
P0300 random misfire diagnostic strategy. Common causes, PIDs to watch, TSBs, and step-by-step isolation of system-wide misfire sources.
Misfire CodesP0301: Cylinder 1 Misfire — Deep Diagnostic Strategy
P0301 cylinder 1 misfire diagnosis for technicians. Swap test methodology, Mode $06 data, secondary ignition analysis, and the cases that don't swap out.
Misfire CodesP0302: Cylinder 2 Misfire — What to Check First
P0302 cylinder 2 misfire diagnosis. Injector diagnostics, balance test, noid light testing, and waveform analysis for injector-related misfires.
Misfire CodesP0303: Cylinder 3 Misfire — Diagnostic Approach
P0303 cylinder 3 misfire diagnosis. Bank-specific V6/V8 strategy, firing order considerations, and bank-isolated testing approaches.
Misfire CodesP0304: Cylinder 4 Misfire — Diagnosis and Causes
P0304 cylinder 4 misfire diagnosis. Compression testing, exhaust backpressure, inline-4 considerations, and GM AFM lifter failure patterns.
Fuel System CodesP0171: System Too Lean Bank 1 — Diagnosis, Causes, and What to Check First
P0171 system too lean bank 1 — full diagnostic walkthrough with fuel trim analysis, common causes, smoke test procedures, and known TSBs. Written tech-to-tech.
Fuel System CodesP0174: System Too Lean Bank 2 — Diagnosis Guide
P0174 system too lean bank 2 diagnostic guide — fuel trim analysis, bank-specific vs system-wide causes, common TSBs, and step-by-step testing. Tech-to-tech.
Fuel System CodesP0172: System Too Rich Bank 1 — What's Dumping Fuel
P0172 system too rich bank 1 — full diagnostic guide covering leaking injectors, purge valves, MAF issues, fuel pressure, and negative fuel trim analysis. Tech-to-tech.
Catalyst CodesP0420: Catalyst System Efficiency Below Threshold Bank 1
P0420 catalyst efficiency diagnosis. What the PCM monitors, causes beyond the cat, O2 sensor checks, and pattern failures by make.
Catalyst CodesP0430: Catalyst System Efficiency Below Threshold Bank 2
P0430 diagnostic guide for technicians. Bank 2 catalyst efficiency diagnosis, O2 sensor analysis, common pattern failures on V6 and V8 engines, and TSBs.
EVAP CodesP0442: EVAP System Small Leak Detected — Finding the Leak
P0442 EVAP small leak diagnostic guide for technicians. Smoke machine techniques, common leak points, purge valve and vent valve testing, and manufacturer TSBs.
EVAP CodesP0455: EVAP System Large Leak — Diagnosis and Causes
P0455 EVAP large leak diagnostic guide for technicians. Common causes from gas caps to purge valves, smoke machine testing, and manufacturer-specific TSBs.
EVAP CodesP0456: EVAP System Very Small Leak — The Needle in a Haystack
P0456 EVAP very small leak diagnostic guide for technicians. Smoke machine techniques for micro-leaks, common failure points, and manufacturer-specific TSBs.
Cooling System CodesP0128: Coolant Temperature Below Thermostat Regulating Temperature
P0128 diagnostic guide for technicians. Thermostat testing, ECT sensor verification, warm-up curve analysis, and common TSBs by manufacturer.
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