Electrical diagnostics
the dealer couldn’t replicate.
Spot-On performs advanced electrical diagnostics for vehicle owners at our San Antonio shop — the faults the dealer or local shop couldn’t isolate. CAN bus communication failures, parasitic battery drains, complex multi-module issues, and the work that ends with someone saying "we can’t replicate it." Manufacturer-grade scan tools, signal analysis, and the patience to chase a reproducible fault until it’s found.
The fault that doesn’t fit on one screen.
- CAN bus issuesMultiple unrelated modules showing communication errors.
- Parasitic battery drainBattery dies overnight or after a few days parked.
- Phantom symptomsHVAC behaving wrong, lighting glitches, accessory issues with no fault code.
Reproducibility first.
Honest advice: please bring the vehicle in actively faulting. Diagnosis is billable time. Faults we can replicate at the bay are the only ones we can resolve cost-effectively.
- Note when it happensTemperature, drive cycle, time of day, what’s running, recent work performed elsewhere.
- Bring it in actively faultingIf the fault is happening when you arrive, we can chase it live — that’s the path to a real answer.
Owners drive in from across the region.
Automotive electrical diagnostics is hands-on, in-shop work, so our customers come to us. Vehicle owners drive in from San Antonio and from nearby Schertz, Selma, Universal City, Helotes, Converse, Leon Valley, Live Oak, and Cibolo, and from farther out — Boerne, Bulverde, New Braunfels, Seguin, San Marcos, Floresville, and Pleasanton — for electrical diagnostics that a dealer or local shop could not finish. Every visit is in-shop, by appointment, at 4715 N Stahl Park, Suite 105, San Antonio, TX 78217. We do not dispatch mobile service to vehicle owners. Shops: see our trade electrical diagnostics page →
Can you find an intermittent electrical fault that only happens sometimes?
Yes, and intermittent faults are most of what our electrical diagnostics work is. An intermittent fault is one that comes and goes: a warning light that appears on cold mornings, a window that quits after an hour of driving. We log live data across a drive cycle, watch the affected circuit on an oscilloscope, and wiggle-test wiring and connectors under load. The more precisely you can describe when it happens, the faster automotive electrical diagnostics gets to the cause.
How do you diagnose a parasitic battery draw?
A parasitic draw is current that keeps flowing after the vehicle is off and asleep, which is why the battery is dead after a night or a weekend. Our electrical diagnostics approach is to measure the key-off current at the battery, let the vehicle go to sleep, then isolate the draw circuit by circuit until one module or accessory is left holding the current. That tells us what is staying awake and why: a stuck relay, an aftermarket accessory, or a control module that will not sleep.
What is a CAN bus or network communication fault?
CAN bus is the wiring network your vehicle's control modules use to talk to each other. When it fails, several unrelated systems throw communication codes at once; ABS, airbag, cluster, and transmission warnings appearing together is the classic sign. Automotive electrical diagnostics for a network fault means checking the bus voltages and termination resistance, finding which module or wiring section is corrupting the network, and proving it before anything is replaced. One chafed wire or one failing module can take down the whole bus.
What if no shop can find my electrical problem?
That is the case we are built for. When a dealer says "we can't replicate it" or a shop has replaced parts without fixing it, the fault usually needs more time and different tools than a general repair visit allows. Our electrical diagnostics work starts from what has already been tried, uses manufacturer-grade scan tools and signal analysis, and chases the fault until it is reproduced and explained. Bring the vehicle in faulting if you can, plus any prior invoices or notes.
Book an in-shop appointment.
Tell us what the vehicle is doing and we’ll have the right tools ready before you arrive.