Auto Electrical & Diagnostics in Rohnert Park & Sonoma County
Rohnert Park Transmission & Auto Repair provides expert electrical diagnostics and repair including check engine light diagnosis, starter and alternator replacement, and computer-based vehicle scanning with ASE certified technicians. We go beyond reading codes — we find and fix the root cause.
Modern vehicles rely on dozens of electronic modules, sensors, and circuits to operate. When something goes wrong in the electrical system, the symptoms can be confusing — a check engine light could mean a hundred different things. Our technicians use professional-grade diagnostic equipment combined with nearly 30 years of experience to isolate problems accurately and repair them efficiently.
Check Engine Light Diagnosis
The check engine light is your vehicle's way of telling you something needs attention. It could be as minor as a loose gas cap or as serious as a catalytic converter failure or engine misfire. The OBD-II system stores diagnostic trouble codes that point our technicians toward the problem — but codes alone do not tell the full story.
We perform comprehensive diagnostics that include code scanning, freeze frame data analysis, live data monitoring, and hands-on component testing. This approach identifies the actual failed component rather than guessing based on a code. A P0420 code, for example, might be a catalytic converter — or it might be an oxygen sensor, exhaust leak, or upstream misfire causing false readings. We find the real problem before replacing anything.
Check Engine Light Service →Starter & Alternator Repair
Your starter motor cranks the engine to life. Your alternator keeps the battery charged and powers all electrical systems while driving. When either fails, you are stuck. A no-start condition is one of the most common electrical complaints we diagnose — and the cause is not always obvious.
We test starter draw, alternator output, and battery health to determine which component has failed. Sometimes what seems like a dead battery is actually a failing alternator that cannot keep it charged. Other times a slow crank points to a worn starter motor rather than a weak battery. Accurate diagnosis saves you from replacing parts you do not need. We stock common starters and alternators for same-day replacement on most vehicles.
Starter & Alternator Service →Computer Diagnostics & Code Reading
Today's vehicles have multiple computer modules controlling engine management, transmission shifting, ABS braking, airbags, climate control, and more. These modules communicate over a network and log faults when something goes out of specification. Our diagnostic tools interface with all major vehicle networks to read codes, monitor live sensor data, and command component tests.
We use professional scan tools — not consumer-grade code readers — that access manufacturer-specific codes, bi-directional controls, and adaptation resets. This means we can command a fuel injector to fire, cycle an ABS valve, or perform a throttle body relearn. Deep diagnostics that pinpoint problems faster and more accurately than code reading alone.
Auto Electrical Repair
Beyond the major components, your vehicle's electrical system includes miles of wiring, hundreds of connectors, fuses, relays, and sensors. Corrosion, rodent damage, water intrusion, and normal wear can cause intermittent or permanent electrical failures. Symptoms range from blown fuses and dead accessories to no-start conditions and warning light clusters.
Our technicians trace wiring issues using wiring diagrams, multimeters, and oscilloscopes. We repair corroded connectors, replace damaged wiring harnesses, diagnose module communication failures, and resolve parasitic battery drains. Whether it is a power window that stopped working or a complex network communication fault, we find and fix it.
OBD-II Code Guides from Our Technicians
Our ATRA and ASE certified technicians write in-depth guides on the most common check engine light codes. These resources explain what each code means, what causes it, and when you need professional repair versus a simple fix you can handle yourself.
P0420 Code Guide
Catalytic converter efficiency below threshold — causes, diagnosis, and repair options.
Check Engine Light After Oil Change
Why your CEL came on after an oil change and what to do about it.
P0300 Random Misfire Guide
Multiple cylinder misfires — spark plugs, coils, fuel injectors, and compression issues.
Top 10 Check Engine Light Codes
The most common codes our technicians see and what they mean for your vehicle.
Related hubs: Transmission | Engine Repair
ASE Certified
Professional-grade diagnostics from certified technicians.
Pro Scan Tools
Factory-level diagnostic equipment for accurate diagnosis.
BBB A+ Rated
Honest diagnostics — we fix problems, not sell parts.
All Makes
Domestic, import, European, hybrid — we diagnose them all.
Electrical & Diagnostic FAQs
Why is my check engine light on?
The check engine light can indicate hundreds of different issues — from a loose gas cap to a failing catalytic converter or misfiring engine. The only way to know for sure is to scan the OBD-II codes with professional diagnostic equipment. We read the codes and perform further testing to identify the root cause, not just the symptom.
How much does a diagnostic scan cost?
We provide professional diagnostic services that go beyond simply reading codes. Our technicians use advanced scan tools, interpret live data, check freeze frame data, and perform hands-on testing to pinpoint the actual problem. Call (707) 584-7727 for current diagnostic pricing.
Can I drive with the check engine light on?
A steady check engine light usually means you can drive safely to the shop for diagnosis. A flashing check engine light means stop driving immediately — it indicates active misfires that can destroy your catalytic converter. When in doubt, call us for guidance.
What are signs my alternator is failing?
Common signs include dimming headlights, a battery warning light on the dashboard, electrical accessories acting erratically, a dead battery that keeps dying after charging, growling or whining noises from the engine area, and difficulty starting. A failing alternator cannot keep your battery charged.
How long does a car battery last?
Most car batteries last three to five years. Hot weather, frequent short trips, and electrical accessory use can shorten battery life. We test battery health and charging system performance to tell you exactly where your battery stands before it leaves you stranded.
What causes parasitic battery drain?
Parasitic drain happens when something continues drawing power after you turn the car off. Common culprits include interior lights staying on, faulty door switches, aftermarket accessories, failing modules, and trunk or glove box lights. We use specialized equipment to isolate the circuit causing the drain.
Is a professional diagnostic better than a parts store code reader?
Parts store code readers only tell you WHAT code is stored. Professional diagnostics tell you WHY. A P0420 code might be a bad catalytic converter, or it might be an oxygen sensor, exhaust leak, or engine misfire causing false readings. We test beyond the code to find the real problem and avoid replacing parts you do not need.
Do you work on hybrid and electric vehicle electrical systems?
Yes. We service hybrid vehicle electrical systems including high-voltage battery diagnostics, inverter testing, and regenerative braking system service. Our technicians are trained on the specific safety procedures required for hybrid and EV work.
Check Engine Light On? We Will Find Out Why.
Professional diagnostics that go beyond reading codes. We find the root cause and fix it right the first time.
Call (707) 584-7727Mon-Thu: 7:30am-5pm | Fri: 7am-4pm | 305 Laguna Dr, Rohnert Park