Symptom Index · Mobile Diagnostics · Hill Country TX
You don't need a code to know something's wrong — but a code is only a starting point either. Each symptom below gets the same honest treatment as the DTC decoder: what it usually proves to be, what a parts-changer will try to sell you, and the test that settles it. Seeing a dashboard light instead of a code? Start there.
Failed your Texas state inspection? There's a guide for that →
An emissions or fuel-trim fault (P0171, P0420, P0442) — system-level, not part-level
A dead coil or plug on ONE cylinder (P0301) — cheap, provable in minutes
Parasitic draw — something staying awake (a trunk light, an amp, a module that will not sleep)
A stored transmission fault (P0700) pointing at a specific sensor or solenoid circuit
No-crank: starter, battery state, ground, or an immobilizer signal — not a new car needed
Air trapped in the system after any coolant work — a bleed job, not a part
Loose, missing, or worn gas cap — genuinely the number-one cause
A weak battery or bad ground making modules brown-out and log phantom U-codes
Pads worn to the wear indicator (the squealer tab) — schedule the job instead of the soundtrack
Worn outer CV joint — clicking tied to steering angle AND throttle load is the signature
Wheel bearing — drone that swells or quiets with gentle swerving, often loudest at 40–60 mph
Glazed or oil-contaminated belt — slips on the ribs, loudest in damp air and at cold start
Lifter tick — oil level, the wrong viscosity, or varnish in the galleries; loudest on cold start
Symptom you don't see listed? A flat $150 mobile diagnostic finds the root cause anywhere in Canyon Lake, San Antonio & Austin — or read a sample report first.
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