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Monday 8am - 5:30pm Tuesday 8am - 5:30pm Wednesday 8am - 5:30pm Thursday 8am - 5:30pm Friday 8am - 5:30pm

https://thompsonautomotiveclinic.com/

Thompson Automotive Clinic, LLC, Flomaton, AL (2026)

05/05/2026

Case Study of the Week
Dr. Diagnostic aka “Dr. D”
’08 Chevy Silverado 1500 5.3L

Customer’s Complaint:
Vehicle will go into reduce power and check engine light will illuminate and customer says that it might go for a while or it might happen shortly after they start driving.

Initial Check:
The problem could be duplicated so I began my diag on the vehicle.

Test:
Battery voltage was good and truck ran well while idling. Couple of aftermarket lights, but nothing to affect the issue that I could see at that time. I did a health scan and received several codes. One was an Evap code, but the 5V1 (P0641) code stood out as the most. After reviewing the codes, it was the 5V code I wanted to check out first. Reviewed the service info first to see what all used the 5V1 reference circuit. After seeing which sensors were on the circuit, I back probed the easiest one to get to, which was the MAP sensor. Used a DVM to check readings first. Key on the meter, read 5V, which was a good reading. Moved the harness around and wiggled connectors. No change in the meter. Changed tools and hooked the scope up and took the truck on a test drive. At a stopped condition, the 5V1 reference was a good 5V, but when the vehicle moved in a forward or reverse motion, I would get an erratic value anywhere between 5V to close to 2 to 2.5V. I can’t remember what time base I had the scope on, but sure it was millisecond per frame.

Fix:
Knowing that the fuel tank pressure sensor was on the list and the route of its circuit, I looked at the harness on the frame and found it rubbing the drive line from the transfer case to the front differential. The harness had been rerouted after a previous repair and had fallen onto the driveshaft. Repaired the wires and the reduced power problem was fixed. This is another one for the books for the oscilloscope. Remember the DVM only shows an average and cannot, will not, show glitches that the ECM will see nor flag.

04/19/2026

We’re excited to share the big news for Thompson Automotive Clinic! My nephew, Austin Minchew, will be joining me on the locksmith side of the business. I’ve known Austin since the day he was born, and have had the privilege to watch him grow into the godly man he is today. I couldn’t be more proud to have him come alongside me. Thankful for God’s timing and looking forward to what He has in store!

04/14/2026

Most know who I am, but for those who may not, sharing our family photo from Easter Sunday. Left to right. Our son, our dil, our grandson, my wife, our granddaughter and myself.

I spent four years in the U.S. Marine Corps as an aircrewman and mechanic on the CH-53 Echo helicopter. After that, I worked across several industrial fields—paper mill, chemical plants and steel.

Along the way, I always had a love for working on vehicles. It started as a side hobby, something I genuinely enjoyed doing in my free time. Over the years, that passion kept growing.

Through prayer and following God’s direction, He opened doors leading me into the automotive world. This began with a brick and mortar automotive shop, which I then later had to close for no longer being able to do the heavy automotive work due to a back injury. Trusting God was still at work, He then led me to mobile automotive diagnostics, programming, automotive locksmith, and planning and designing automotive training classes for automotive technicians for small shops and independent auto sales companies.

What began as a hobby became my calling, and I’m thankful every day to serve you and others using the skills and path He’s given me.

04/14/2026

Case Study of the Week
No Crank / No Start

15 Chevy Silverado

Customer’s Complaint:
Randomly will not crank, just makes a clicking sound outside under the hood. Then the other times, it cranks and starts up fine.

Customer took the truck to the dealership and had them make a key because the customer thought it was in theft mode when it would not crank and start.

Test:
After confirming the problem / complaint, I started checking the starting system. Battery voltage was 12.4V at the battery. Check for voltage drop on the B+ wire to the starter for voltage drop and it was ok. Checked the starter command signal at starter for voltage and for voltage drop and had very low reading on command signal. I then knew it had a ground issue, and I did a quick bypass on the ground side. I used a set of cables and put one end on negative post and the other end to the engine block. The truck immediately started. Took cables off and it is clicking again. Found ground on motor loose and after moving it around a little, truck would start but still had about a1V drop on ground. After tightening the ground bolt, the voltage drop was normal and truck was fixed.

Fix:
Tightened main engine ground.

Lesson:
Unwanted resistance = voltage drop on Positive side or Negative side. It does not matter.

04/11/2026

Coming soon!

I’ve got someone special joining me to help meet the growing needs on the locksmith side. I couldn’t be more honored to have him on board! I’ll be announcing who it is next week.

Final touches are being done on the van to be road ready! Once complete, the business contact number will be shared. Stay tuned and thank you all for your continued support!

09/26/2025

Case Study of the Week

2019 Hyundai Santa Fe

I apologize in advance for this lengthy explanation. It will be worth taking time to read. This Case Study will be separated into two Customer’s Complaints (same customer and same problem), Initial Checks, Tests, and Fixes.

Customer’s Complaint:
Vehicle will display several warning lights on cluster and vehicle will still run, but has shifting problems, RPM, fuel gauge inop, airbag, side object, hill decent.

Initial Check:
Visited this vehicle several times, but the faults would not be active upon first couple of diagnostic attempts. Codes would reveal about eight modules not communicating and flagging U-codes for it. Finally got vehicle and brought it to my house and attempted to get the vehicle to go into its fault condition. After checking it in late evening time, finally able to get the faults to be duplicated.

Test:
After looking at data and many circuits tested, it was determined that all of the P-CAN bus modules were going offline. Checked again the next morning and vehicle operated fine again. I discovered that the fault would occur after the lights were turned on, or daytime running lights cut off in the late evening time due to daylight sensor.

Fix:
After reviewing wiring diagrams and other testing of circuits, I determined that the IBU module was the problem and replaced it with a new module. Repair fixed the problem and vehicle was delivered back to customer (TO BE CONTINUED).

*Three months later the dreaded phone call. The original problem was back.*

Customer’s Complaint:
Same faults, same conditions to make the faults occur.

Test:
More testing and several phone calls with a Hyundai tech on a diagnostic tech support, determined the P-CAN bus was still shorting to voltage when lights were coming on or daytime running lights went off because of the daylight sensor. The culprit was finally located under the center console and under gear shifter on the floor. In a nice little indention, sat a junction connector with P-CAN data wires and illumination wires joined (shorted) together with Coke, Pepsi, or maybe Dr. Pepper syrup, not sure, which apparently is a particularly good conductor.

So now after finding this, the problem makes sense. With lights on or daytime running lights cutting off, all of the interior illumination lights would come on and short the P-CAN data circuit to voltage.

Fix:
Repaired connector and the problem was fixed for real this time.

Lost a lot of sleep over this one.

08/01/2025

Case Study of the Week

2019 Honda Civic

Customer’s Complaint:
Crank, but no start condition

Initial Check:
Vehicle was just purchased and only came with one key. A second key was purchased and programmed for a spare. Vehicle performed as it should with both keys, the original was used, and new key put up for spare. Brought vehicle home and parked. Returned to vehicle later and here is where the diag of the week started. Before trying to start the car, a ring of diamond ascents was placed on the face of the ignition lock cylinder. After a short time, the vehicle was attempted to be started, and it would crank but not start.

Test:
Initial test complaint could be duplicated, and the vehicle would not start. The battery voltage was low, so a jump box was placed on the battery. Scan data revealed no codes. Noticed theft light flashing slowly. Checked both keys and immobilizer function of the vehicle. No codes, but showed a system malfunction after running a system check. After checking key in ignition signal to immobilizer module and signal not being generated, removed the decorative ring around the ignition lock cylinder. Signal returned and vehicle started up. Checked the starting abilities with both keys and vehicle was operating fine.

Fix:
The fix came during the test. In review, the decorative ring did not interfere with the key turning but it did something to the chip signal to the immobilizer module. Could it be the decorative crystals messing with the signal? That’s my belief.

08/01/2025

Case Study for Last Week

2015 Chevrolet Tahoe

Customer’s Complaint:
Check engine light on, but vehicle seems to run ok after the motor had been swapped at a shop.

Initial Check:
Complaint can be duplicated. The code was present, looked at freeze frame data and cleared code. It would return as soon as the vehicle was started.

Test:
Read the criteria for the code to set. P0341 cam position range/ performance code. Scan data showed Cam position 0 and engine RPM data at 0. No movement with engine load applied. Viewed wiring diagram for Cam signal input at ECM. Set scope up and took readings of the CAM at the ECM by back probing Cam signal pinout. Signal looked good. Waveform had a signal and looked normal. Acquired a known good Cam waveform and the problem revealed itself. View the following pictures. The first picture is the actual vehicle data. The second picture is the known good (red waveform trace is the good Cam sensor signal, disregard the blue trace that is a crank sensor waveform). Leave a comment and what you think the problem is. I apologize for the glare in the first photo.

07/17/2025

Case Study of the Week
"It’s Always the Easy Ones that Get You"

97 Pontiac Grand Prix

Customer’s Complaint:
AC Blower motor is inoperative in 1, 2, 3, 4 fan speed positions. Runs fine on high.

Initial Check:
Complaint can be duplicated.

Test:
Car battery and voltage check was good. Looked at scan data to see if any codes could be related to the problem. Looked at wiring diagram and service info for operation and description. Started checking circuits and fuses, powers and grounds. Checked for resistor change by the switch at the blower motor resistor and relay. The resistor was in a bad location under the glove box close to the firewall and hard to back probe. Here is where my mistake happened. I unplugged it for easy access. Circuit check good for each switch position. Control switch was working properly and voltage was being supplied on each wire to the resistor / problem solved / need a resistor “wrong”. Missed diagnosed this because of one of the most important test procedures while testing circuits, “Test Them Under a Load”. There was a bad voltage drop from the ignition switch to the fuse box on the two fuses that supplied the voltage to the circuit. Under a load there was not enough voltage to run the fan, but checked unloaded, the voltages looked fine.

Fix:
It needed a new ignition switch because the circuit supplied voltage comes from the ignition switch to the fuse block, which then supplies power to the blower motor speech controls.

07/09/2025

Case Study of the Week

10 Ford F-150, 4.61, 2wd

Customer’s Complaint:
Front left turn signal inop with the headlights on. Headlights off left turn signal works fine.

Initial Check:
Complaint can be duplicated. Headlights are aftermarket LED Bulbs. Turn signal bulbs were the correct bulbs. No accessory were present in the wiring.

Test:
Looked at wiring diagram and service info for operation and description for the turn signal. First test – check battery voltage and it was within specifications. Did a full vehicle health scan to determine if there were any codes related to this condition. Then checked for battery + (voltage) at turn signal with turn signal switch commanded on. Battery voltage was at turn signal bulb on positive side of terminal at connector. Checked for ground on the ground side of bulb and battery voltage was also present there. After examining wiring diagram again, determined ground was a chassis ground and it was broken (open circuit). Repaired ground and turn signal works as it should.

Question:
Why did the turn signal work with the lights off but not on?

Answer: With the lights off, the park lamp relay is open, which allows the turn signal circuit to use the grounds from other circuits positive side while the battery voltage is off those circuits.

07/08/2025

I am starting a new addition to my business, Thompson Automotive Clinic. God has been opening this path throughout the past year. I have been planning and designing automotive training classes for small shops and independent auto sales companies. I see a great need for training and as automotive technicians, we need to stay up to date with all the innovative technology that is continuously coming out each year and through the year. I have several in shop classes ready now and more in progress. I also have access to a lot of trainers throughout the states with advanced training courses, which will be held in a larger classroom setting. I also intend to post a weekly diagnostic case study on Facebook for those that are interested.

In Shop Classes – Up to 4 Technicians
*Basic Automotive Electrical and Troubleshooting
*Understanding Wiring Diagrams
*The Diagnostic Strategy
*Understanding Sensors and Operation

Advanced Classes – Up to 25 Technicians
*Communication Network
*Oscilloscope Set-up and Use
*Engine Performance
*ADAS Training
*Module Programming
*Ford Transmission Diagnostic & Repair

Contact me for more details and scheduling. Stay tuned for more classes. Please feel free to send any inquiries on classes that you would like for your shop.

Thompson Automotive Clinic, LLC

05/05/2026

04/19/2026

04/14/2026

04/14/2026

04/11/2026

09/26/2025

08/01/2025

08/01/2025

07/17/2025

07/09/2025

07/08/2025

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Monday	8am - 5:30pm
Tuesday	8am - 5:30pm
Wednesday	8am - 5:30pm
Thursday	8am - 5:30pm
Friday	8am - 5:30pm