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 real problems hide.
Diagnostic Trouble Codes
P0016 Crankshaft/Camshaft Correlation — What's Causing It
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 and Why
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 — How to Find and Fix the Fault
P0340 camshaft position sensor circuit diagnosis. CMP sensor scope testing, wiring faults, reluctor damage. Pattern failures on Nissan, Ford, Jeep, GM.
Misfire CodesP0300 Random Misfire — Causes and Diagnostic Approach
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 — Swap Test, Mode $06, and Beyond
P0301 cylinder 1 misfire diagnosis — swap test methodology, Mode $06 data, secondary ignition analysis, and the cases that don't swap out.
Misfire CodesP0302 Cylinder 2 Misfire — Injector Testing and Mechanical Diagnosis
P0302 cylinder 2 misfire diagnosis. Injector diagnostics, balance test, noid light testing, and waveform analysis for injector-related misfires.
Misfire CodesP0303 Cylinder 3 Misfire — Bank Assignment and Diagnostic Strategy
P0303 cylinder 3 misfire diagnosis. Bank-specific V6/V8 strategy, firing order considerations, and bank-isolated testing approaches.
Misfire CodesP0304 Cylinder 4 Misfire — Compression, AFM Lifters, and Exhaust Restriction
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 — What Fuel Trims Are Telling You
P0171 system too lean bank 1 — fuel trim analysis, vacuum leak testing, MAF diagnosis, and known TSBs. Step-by-step for technicians.
Fuel System CodesP0174 System Too Lean Bank 2 — Bank-Specific vs. System-Wide
P0174 system too lean bank 2 — fuel trim analysis, bank-specific vs. system-wide causes, step-by-step diagnosis, and known TSBs.
Fuel System CodesP0172 System Too Rich — Negative Fuel Trims and What's Dumping Fuel
P0172 system too rich bank 1 — leaking injectors, purge valve, MAF issues, fuel pressure, and negative fuel trim analysis.
Catalyst CodesP0420: Catalyst System Efficiency Below Threshold Bank 1
P0420 catalyst efficiency code — what the PCM monitors, 7 causes beyond the cat, O2 sensor diagnosis, repair costs, and pattern failures.
Catalyst CodesP0430 Bank 2 Catalyst Efficiency — Why Bank 2 Fails First
P0430 bank 2 catalyst efficiency — O2 sensor analysis, Mode $06 data, pattern failures on GM, Ford, and Nissan V6/V8 engines.
EVAP CodesP0442 EVAP Small Leak — Finding It When the Smoke Machine Can't
P0442 EVAP small leak — smoke machine techniques, FTP sensor diagnosis, purge valve testing, vent valve testing, and manufacturer-specific TSBs.
EVAP CodesP0455 EVAP Large Leak — From Gas Cap to Purge Valve
P0455 EVAP large leak — gas cap, purge valve, vent valve, disconnected hoses, and FTP sensor testing. Manufacturer-specific TSBs included.
EVAP CodesP0456 EVAP Very Small Leak — The Hardest EVAP Code to Diagnose
P0456 EVAP very small leak — smoke machine techniques for micro-leaks, temperature-dependent diagnosis, FTP sensor monitoring, and 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.
Symptom Diagnostics
Engine Won't Start — No Crank Systematic Diagnosis
Engine won't start no crank — battery, starter circuit, security, neutral safety switch, and wiring. Systematic diagnosis from a Master Tech.
Symptom DiagnosisEngine Cranks but Won't Start — Fuel, Spark, or Compression?
Engine cranks but won't start — check fuel, spark, compression, and timing. Step-by-step crank no-start diagnosis from a 25-year Master Tech.
Symptom DiagnosisBrake Pedal Pulsation — Finding the Real Cause
Brake pedal pulsation diagnosis — disc thickness variation, lateral runout, caliper issues, and measurement procedures. Real causes explained.
Symptom DiagnosisPower Steering Whine — Pump, Fluid, Rack, or Something Else?
Power steering whine diagnosis — pump noise, low fluid, aerated fluid, rack leaks, and belt issues. Hydraulic and electric PS covered.
Symptom DiagnosisCar Shakes at Idle — Systematic Diagnosis for a Rough Idle
Car shakes at idle diagnosis — vacuum leaks, misfires, throttle body, IAC, motor mounts, and carbon buildup. Systematic rough idle guide.
Symptom DiagnosisEngine Overheating — Systematic Cooling System Diagnosis
Engine overheating diagnosis — coolant level, thermostat, water pump, radiator flow, head gasket testing, cooling fans, pressure test, and air bleeding.
Symptom DiagnosisTransmission Slipping — Systematic Diagnosis for Automatic Transmissions
Transmission slipping diagnosis — fluid check, scan tool data, TCC shudder vs. internal slip, valve body, clutch pack wear, and adaptive reset.
Symptom DiagnosisABS Warning Light On — Systematic Diagnosis
ABS warning light diagnosis — read ABS DTCs, wheel speed sensor testing, tone ring inspection, ABS module, hydraulic modulator, and wiring.
Advanced Diagnostic Techniques
Beyond the scan tool — the tools and methods that separate a parts changer from a diagnostician.
PicoScope Automotive Diagnostics — Complete Guide
Lab scope setup, waveform capture, secondary ignition, relative compression, NVH vibration analysis, and parasitic draw testing.
Thermal ImagingThermal Camera Diagnostics — See What You Cannot See
Thermal imaging for electrical faults, misfires, cooling system issues, brake drag, HVAC diagnosis, exhaust leaks, and water leaks.
Scope FundamentalsOscilloscope Basics for Automotive Technicians
When to use a scope vs. a multimeter, basic waveform patterns, setup, and building your pattern library.
NetworkCAN Bus Diagnostics — Vehicle Network Testing
CAN bus physical layer testing, waveform analysis, network fault isolation, and U-code diagnosis.
ElectricalVoltage Drop Testing — Find What the Meter Misses
Voltage drop testing on power and ground circuits under load — the most underused test in the shop.
Fuel SystemFuel Trim Diagnostics — Reading the Numbers
Short-term and long-term fuel trim analysis. What the numbers mean and how to use them to find the root cause.
StrategyComponent Swap Testing — Eliminate Variables the Right Way
When to swap, what to swap, how to track results, and what to do when the swap test does not solve it.
ElectricalJumper Wires & Relay Bypass — Circuit Verification
Safe jumper wire techniques, fused bypass testing, relay socket testing, and ground verification methods.