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Computer Diagnostics

Electrical Diagnosis at Johnny's Automotive

Electrical gremlins that come and go are the hardest kind to catch. Here's what a booked diagnostic session looks like, and what you get at the end of it.

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ASE Certified TechniciansFlexible Drop-Off Hours20+ Years
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Why does my car's electrical problem only happen sometimes?

An electrical diagnosis is a booked block of time, not a quick look under the hood. Intermittent faults don't perform on command, so the session is built around catching one in the act instead of hoping it shows up while you wait.

It starts with you. The most useful thing you can bring is the story: when it happens, what else was running at the time, whether it's worse cold or after a long drive, whether rain or a car wash changes anything, and whether it started right around the time something else got installed or replaced. A driver who says "only on right turns, only with the AC on" has already narrowed the search more than any tool can.

From there we scan every module on the vehicle, not just the engine. Modern cars carry a dozen or more computers talking to each other, and a fault stored in a body module or a network communication code is often the thread that explains a symptom the engine module never saw. We pull stored codes, pending codes, freeze frame data, and network status, then read them as a group rather than chasing whatever sits at the top of the list.

Then the hunting starts. Wiggle tests on suspect connectors and harness sections while we watch live data. Recording the data stream so a fault that lasts half a second still leaves a fingerprint. When a problem only turns up overnight or after the car has sat for hours, we can leave monitoring connected and let the car tell on itself.

What you get back is a written result: what we tested, what the numbers say, the named cause, and what the repair involves. Deciding on that repair is a separate conversation.

Where we work

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Haines City, FL

Haines City, FL

4.8 (2,060) as of Oct 20264.8 out of 5, from 2,060 Google reviews, as of October 2026

31600 U.S. 27

Mon to Fri, 7:30 AM to 5:30 PM

Electrical Diagnosis hereCall (863) 422-2995Directions
Frostproof, FL

Frostproof, FL

4.8 (161) as of Oct 20264.8 out of 5, from 161 Google reviews, as of October 2026

101 North Scenic Highway

Mon to Fri, 7:30 AM to 5:30 PM

Electrical Diagnosis hereCall (863) 546-6735Directions
Lake Wales, FL

Lake Wales, FL

4.8 (537) as of Oct 20264.8 out of 5, from 537 Google reviews, as of October 2026

323 North Scenic Highway

Mon to Fri, 7:30 AM to 5:30 PM

Electrical Diagnosis hereCall (863) 676-3858Directions
Sebring, FL

Sebring, FL

4.6 (170) as of Oct 20264.6 out of 5, from 170 Google reviews, as of October 2026

435 North Orange Street

Mon to Fri, 7:30 AM to 5:30 PM

Electrical Diagnosis hereCall (863) 471-0044Directions
Wauchula, FL

Wauchula, FL

4.9 (31) as of Oct 20264.9 out of 5, from 31 Google reviews, as of October 2026

201 North 6th Avenue

Mon to Fri, 7:30 AM to 5:30 PM

Electrical Diagnosis hereCall (863) 222-3947Directions
Winter Haven, FL

Winter Haven, FL

4.8 (586) as of Oct 20264.8 out of 5, from 586 Google reviews, as of October 2026

5100 Dundee Road

Mon to Fri, 7:30 AM to 5:30 PM

Electrical Diagnosis hereCall (863) 949-2995Directions
Diagnostics

Problems we fix

Our experts diagnose and resolve any issue.

Dash lights flicker on rough roads

Usually a ground connection or a chafed section of harness that only loses contact when the body flexes. The fact that bumps trigger it is a clue worth following, not background noise.

Something works, then doesn't, then works again

Often a connector with a spread terminal or a corroded pin. Under a wiggle test it will usually repeat on demand, which is how it gets confirmed instead of assumed.

It only acts up when the car gets wet

Water finding its way into a connector, a body seal, or a light housing. We can recreate those conditions in the bay rather than wait around for the next storm.

Warning lights come on in groups for no reason

Typically one problem upstream of several modules, making all of them complain at once. Scanning everything is what turns five confusing symptoms into one cause.

It started right after other work was done

Frequently something disturbed during that job: a connector not fully seated, a pinched wire, a ground left loose behind a bracket. Tell us that timing at drop-off, it shortens the search a lot.

Nobody can make it happen in the shop

This is exactly why recording and overnight monitoring exist. Intermittent doesn't mean unfindable, it means the answer needs time and data instead of a quick test drive.

Reviews

What customers say about our electrical diagnosis work

I took my H3 in for electrical and safety issues. The service was exceptional! Great shout out to Jeffrey for having the most amazing customer service at the Winter Haven location. My truck had to be kept overnight and they gave me a loaner car. I have never experienced this at any other mechanic shop which puts them above the rest! My truck was successfully completed in a timely manner. If I could give more than 5 stars I would

TALITA JOHNSON SMITH

Verified Google Review

My car was having an electrical issue, causing the hatchback on my Chevy Equinox to not open. Identifying the problem was lengthy but the mechanics/technicians have successfully identified all 3 areas that needed work and they have fixed the problem. They initially identified several other mechanical issues that needed attention. Since my husband had previously noted that maintenance in these particular areas was needed, we never got the impression they were pushing to upsell their services to us. The final bill was the same as the initial estimate that was presented to us. The Super Clean facility was a delight to experience. The staff is professional and polite.

J McGahen

Verified Google Review

My 2018 Subaru Forester had begun to stall out at unexpected times, and despite many attempts to resolve the issue on my own, nothing seemed to work. Anticipating a very high bill for repairs, I decided to try Johnny's Automotive before taking the vehicle to the service department at the dealership for what I knew would be a VERY expensive repair plus sales pitches for all kinds of other issues presented as urgent matters. Well, to my surprise and delight, Johnny's was able to make the repair for a very affordable price. Most of my issues were related to squirrels who had managed to infiltrate the electrical system of the car and chew through a number of wires. Because of Johnny's pledge not to rip its customers off, I decided to have them to do an oil change (cheaper than even all of those quick oil change shops that pop up along major highways) and add refrigerant to my AC which had not been cooling as efficiently as before. Johnny's is now my "go-to" service facility when my vehicle requires some TLC. I highly recommend Johnny's Automotive!!! UPDATE: Johnny's Automotive of Lake Wales continues to please! This time--December 30, 2024--I took my Subaru in for an oil change and tire rotation, along with a request for an analysis for an electronic problem. Great service along with gracious employees make for a wonderful experience. As my vehicle is getting a little age on it, there were other services that should be performed in the near future. The personnel there explained those recommendations clearly. After I "recover" from my holiday spending spree, I'll definitely take it back for those services to be performed. Unless Johnny's is ever "stumped" over a problem--which, really, I don't anticipate--I am hoping never to take my vehicle to the dealership's service center again! I trust Johnny's to be honest about any problems they diagnose, along with accurate quotes about pricing to resolve those problems--without extraneous "upsell" speeches, like one gets at dealership service centers!

Dann Hazel

Verified Google Review

I am a snowbird coming to Florida from Canada for the winter. I had an electrical issue with my car this year on the way down and did some research looking for a good repair place to take it. I found Johnny's and glad I did. They found my issue quickly and fixed it as part of their assessment process. They thoroughly inspected my car as part of this process and pointed out any issues they found that needed attention at some point soon. They are very thorough! I am very happy with their work and would recommend them to anyone. I certainly will go back when I need service. Thanks to all the friendly courteous staff there especially Brandon who did the work and Sahra the adviser!

Robert Smith

Verified Google Review

Car broke down Christmas Eve and AAA came to give a jump, but could not & said it was Alternator & Battery. Few days later AAA recommended Johnny’s Automative so had it towed to Haines City. When I called that car was on its way, I asked they also check Air Conditioning. Mike called back the next day to advise it was not the Alternator, but it was battery. He gave me costs and agreed to go ahead with repairs. He sent me pictures and kept me informed with other issues. This car has not been looked at for about 3 yrs, so was not surprised it needed brake work. Mike at Johnny’s Automotive was great. I was very impressed with how he kept me updated on every step of the way. I would definitely recommend Johnny’s Automotive in Haines City

Betty Russo

Verified Google Review

Had an electrical issue on my Santa Fe and Kevin nailed it. Great Mechanics, Great staff, Great Price & Great Work! Thanks.....

Rick DePalma

Verified Google Review

FAQ

Electrical Diagnosis questions, answered

Common questions about our electrical diagnosis services.

How long does an electrical diagnosis take?

It depends on how cooperative the fault is. Something we can reproduce in the bay is often sorted inside a single session, while a problem that shows up twice a week may need the car with us longer or a monitoring setup. We'll tell you which situation you're in before we start.

What should I tell you when I drop the car off?

Everything you've noticed, including the parts that sound unrelated. When it happens, what's switched on at the time, the weather, the road, how long the car had been running. Those details aim the testing in a direction, and no scan tool can give us that.

Can I wait for it, or do I need to leave the car?

For anything intermittent, plan on leaving it. Catching a fault that appears on its own schedule takes more time than a waiting room visit allows, and rushing that step is how the wrong part gets replaced.

Will I get a specific answer or just a general area?

The goal is a named cause, not a category. You get the readings we took, the point where the system stops making sense, and what the repair involves. If a session doesn't get us all the way there, we'll say so plainly instead of guessing.

My check engine light isn't on. Is scanning still worth it?

Yes, and often more so. Plenty of electrical faults never set an engine code because they live in the body, chassis, or network modules. Scanning all of them is the only way those show up at all.

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ASE Certified Technicians

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20+ Years

2 decades of trusted service