Engine Diagnostics in The Dominion, TX Precision diagnostics. Mobile convenience.

What Your Check Engine Light Is Actually Telling You

The check engine light doesn't mean your engine is about to explode — but it does mean something in your powertrain or emissions system triggered a fault code, and that code is stored in your vehicle's ECU right now, waiting to be read. The problem is that a generic code reader from AutoZone only tells you what failed — not why. P0420 means catalyst efficiency is low. It doesn't tell you if it's a dying catalytic converter, a bad oxygen sensor, an exhaust leak, or engine oil burning into the exhaust stream.

That's the difference between a parts-store scan and a professional diagnostic: root-cause analysis, not just code retrieval.

What a Mobile Engine Diagnostic Covers

Danny arrives with a bi-directional OBD2 scanner that reads all control modules — not just the engine. He pulls live sensor data: oxygen sensor switching speed, fuel trim percentages, MAF airflow values, and misfire counters. He captures freeze-frame data that shows exactly what your engine was doing when the fault triggered. For intermittent faults that don't always set a code, this freeze-frame data is often the only way to reproduce the condition without hours of test driving.

You receive a written summary of findings with prioritized repair recommendations. No upselling. No "you need to leave the car" delays. Most diagnostics wrap up in 45–90 minutes at your location.

The $75 Diagnostic Fee — Here's How It Works

The diagnostic fee is $75 flat. If you hire Danny to complete the repair at the same visit, the full $75 is credited toward your repair total. You only pay the standalone diagnostic fee if you choose not to proceed with the repair — which is always your decision, with no pressure.

Most shops charge $100–$150 for a diagnostic and don't credit it toward anything. Dealerships often charge $175+ just to pull codes and write up an estimate.

Common Check Engine Codes We Diagnose in San Antonio

P0300–P0308 random or cylinder-specific misfires, P0420/P0430 catalyst efficiency, P0171/P0174 lean fuel trim (vacuum leaks, MAF issues), P0455/P0442 EVAP system leaks (often just a loose gas cap, but not always), P0128 thermostat operation, and transmission codes P07xx–P08xx across all domestic and import makes. We also read ABS, SRS airbag, TPMS, and body control modules — most shops only read engine codes.