23/07/2026
One thing I've learned in automotive diagnosis is this:
When you're sure of your diagnosis, people cannot easily confuse you.
A few years ago, I was called to check a 2007 Toyota RAV4 that would not start.
I started with the basics. There was no spark and the injectors were not operating. After testing the circuits, I discovered the crankshaft sensor was not receiving the correct signal because the engine control module (PCM/ECM) had an internal fault.
I repaired the PCM, and immediately the spark returned and the injectors started working.
But the engine still refused to start.
I asked the mechanic, What happened before this problem started?
He said, We just overhauled the engine. Before the overhaul, it only had engine smoke.
At that point, I knew the electrical problem had been solved. I told them the remaining fault was related to the engine rebuild.
They argued with me.
They checked the timing and said it was correct. Some even suggested that maybe the repaired PCM was still bad and should be replaced.
I said, No. The PCM is doing its job now. The problem is inside the engine.
After much discussion, they finally removed the engine again to inspect it.
A few days later, one of the mechanics saw me and said, Sir, you were right.
They found that the new piston rings had seized in the pistons. The rings were so tight they had to use a hammer to remove them. That was why the engine couldn't build compression properly, even though the electrical system was working.
That day taught me a lesson I'll never forget:
When your diagnosis is based on proper testing, stand by it.
People may doubt you. They may suggest replacing parts that are not faulty. But if your conclusion is backed by evidence, don't let pressure change your diagnosis.
Confidence should come from testing, not from guessing.
That is what separates a parts changer from a true diagnostic technician.
Have you ever stood by your diagnosis even when everyone disagreed? Share your experience in the comments.