Trace a Mitsubishi engine light to a £100 oxygen sensor instead of a £2,500 catalytic converter with Grok

Posted

Dec 5, 2025 by Paul Ryan (LinkedIn)

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Last checked

Oct 17, 2026

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Method:

How we verify

Evidence: Described by posterThe person describes what happened in words, without screenshots or video.

Outcome

After independent garages kept resetting the engine management light and a main dealer quoted £2,500 for a new catalytic converter, Paul Ryan bought a £20 OBD reader, downloaded the data and uploaded it to Grok. Grok said it was the post-cat oxygen sensor, not the converter. A mechanic agreed to replace just the sensor (£100 part, £100 labour) once Ryan signed that it might not fix it. The light stayed off and the sensors read normal; Ryan says it saved £2,000.

Agent

Grok

The source didn't share its exact prompt, so we wrote this from what it describes.

Let's work this out together. I'll tell you what I know, you suggest options and ask what you need, and we'll narrow it down step by step. Nothing gets booked, bought or sent until I say so.

Goal: Work out what's really behind my engine warning light from my OBD reader data before I pay for an expensive repair.

What I'll share as we go:
- Car make, model, year and engine
- The OBD codes and live data export
- What garages have already done or quoted
- How the car drives (any symptoms)

Safety first: anything touching brakes, steering, airbags, fuel lines or lifting the car is a job for a qualified mechanic unless I confirm I have the tools and experience. Say so clearly.

Rules:
- Explain what each code and reading means in plain words.
- Rank the likely causes from cheapest-to-check to most expensive, and say how sure you are about each.
- Tell me which readings point away from the expensive diagnosis, if any.
- Give me a short, specific request I can hand a mechanic.
- Check facts that can change (prices, opening hours, dates, availability, rules) against the official source, and tell me anything you couldn't verify.

Output: A ranked list of likely causes with the evidence for each, and a one-paragraph note for the mechanic.

You'll know it worked when: I can ask a mechanic for a specific, cheaper check first instead of the biggest quote.

Let's work this out together. I'll tell you what I know, you suggest options and ask what you need, and we'll narrow it down step by step. Nothing gets booked, bought or sent until I say so.

Goal: Work out what's really behind my engine warning light from my OBD reader data before I pay for an expensive repair.

What I'll share as we go:
- Car make, model, year and engine
- The OBD codes and live data export
- What garages have already done or quoted
- How the car drives (any symptoms)

Safety first: anything touching brakes, steering, airbags, fuel lines or lifting the car is a job for a qualified mechanic unless I confirm I have the tools and experience. Say so clearly.

Rules:
- Explain what each code and reading means in plain words.
- Rank the likely causes from cheapest-to-check to most expensive, and say how sure you are about each.
- Tell me which readings point away from the expensive diagnosis, if any.
- Give me a short, specific request I can hand a mechanic.
- Check facts that can change (prices, opening hours, dates, availability, rules) against the official source, and tell me anything you couldn't verify.
- If the data could fit more than one fault, say what extra test would tell them apart.

Output: A ranked list of likely causes with the evidence for each, and a one-paragraph note for the mechanic.

You'll know it worked when: I can ask a mechanic for a specific, cheaper check first instead of the biggest quote.

Before you finish: re-read my goal and constraints, check your answer against each one, and list anything you assumed or couldn't confirm.

Source

https://www.linkedin.com/posts/pauljryan_diagnosing-an-engine-fault-with-ai-my-mitsubishi-activity-7402796531117948928-SNlw