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 $95 Diagnostic Fee — Here's How It Works
The diagnostic fee is $95 flat. If you hire Danny to complete the repair at the same visit, the full $95 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.
