Gemini vs ChatGPT on a check-engine EVAP code: replace the sensor or clear the code?
- Posted
- by Cody Hoeft (LinkedIn)
- Last checked
- Method:
- How we verify
Evidence: Described by posterThe person describes what happened in words, without screenshots or video.
Outcome
After a check-engine light on his pickup, a driver read one evaporative-system code and the sensor readings, then asked Gemini and ChatGPT what they meant. Gemini suggested replacing the sensor; ChatGPT said to clear the codes and see if they came back. He cleared them, and after a long trip the code hadn't returned, avoiding a costly, labour-heavy part replacement for now.
Agent
Prompt Recreated prompt
The source didn't share its exact prompt, so we wrote this from what it describes.
Run this task now, exactly as written below. Everything you need is here, so start straight away and only stop if something required is missing or a rule below tells you to. Goal: Interpret a check-engine code and sensor readings, and tell me the least-cost safe next step. Fill in before running: - Vehicle: [MAKE MODEL YEAR] - Code(s) and freeze-frame or sensor readings: [PASTE] - Basic checks done (oil, coolant, gas cap): [LIST] 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 the code means and how serious it is. - Give the cheapest reasonable next step first (e.g. clear and monitor) and when that's not safe. - List what would justify replacing a part. - Tell me what to watch for after clearing the code. - If a site asks for a login, a CAPTCHA or payment details, stop and hand control back to me. - Ask for my OK before you pay, book, send, submit or cancel anything. - Check facts that can change (prices, opening hours, dates, availability, rules) against the official source, and tell me anything you couldn't verify. Output: Code explanation, risk level and a step-by-step plan. You'll know it worked when: the light stays off, or I know exactly which part to test or replace.
Customize this prompt
Answer these questions and we'll put your answers into the prompt for you. You can leave any of them empty.
e.g. 2018 Honda Pilot
Your prompt
Run this task now, exactly as written below. Everything you need is here, so start straight away and only stop if something required is missing or a rule below tells you to. Goal: Interpret a check-engine code and sensor readings, and tell me the least-cost safe next step. Fill in before running: - Vehicle: [MAKE MODEL YEAR] - Code(s) and freeze-frame or sensor readings: [PASTE] - Basic checks done (oil, coolant, gas cap): [LIST] 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 the code means and how serious it is. - Give the cheapest reasonable next step first (e.g. clear and monitor) and when that's not safe. - List what would justify replacing a part. - Tell me what to watch for after clearing the code. - If a site asks for a login, a CAPTCHA or payment details, stop and hand control back to me. - Ask for my OK before you pay, book, send, submit or cancel anything. - Check facts that can change (prices, opening hours, dates, availability, rules) against the official source, and tell me anything you couldn't verify. Output: Code explanation, risk level and a step-by-step plan. You'll know it worked when: the light stays off, or I know exactly which part to test or replace.
Scroll to see the whole prompt. Your answers show in green.
3 blanks are still empty: Vehicle; Code(s) and freeze-frame or sensor readings; Basic checks done (oil, coolant, gas cap). They'll stay in brackets in your prompt, so the chat tool may ask you about them.
What you type stays in this browser tab. We don't send it or save it, and it's gone when you leave the page. If you use a "Try this in" button, your answers go to that tool as part of the prompt.
Try this in:
This prompt has blanks to fill in, like [MAKE MODEL YEAR]. We'll copy it instead of filling it in, so you can edit it before you send.
Opens in a new tab. We don't see what you send.
These links are only a shortcut. We're not affiliated with OpenAI, Google or xAI, and your results may not match the source.
Optional stronger version
Our rewrite with extra checks. The poster didn't test it.
Run this task now, exactly as written below. Everything you need is here, so start straight away and only stop if something required is missing or a rule below tells you to. Goal: Interpret a check-engine code and sensor readings, and tell me the least-cost safe next step. Fill in before running: - Vehicle: [MAKE MODEL YEAR] - Code(s) and freeze-frame or sensor readings: [PASTE] - Basic checks done (oil, coolant, gas cap): [LIST] 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 the code means and how serious it is. - Give the cheapest reasonable next step first (e.g. clear and monitor) and when that's not safe. - List what would justify replacing a part. - Tell me what to watch for after clearing the code. - If a site asks for a login, a CAPTCHA or payment details, stop and hand control back to me. - Ask for my OK before you pay, book, send, submit or cancel anything. - Check facts that can change (prices, opening hours, dates, availability, rules) against the official source, and tell me anything you couldn't verify. - Ask a second assistant or a mechanic when the answers disagree, as this poster did. Output: Code explanation, risk level and a step-by-step plan. You'll know it worked when: the light stays off, or I know exactly which part to test or replace. 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
Related cases
- Fix check-engine lights on three vehicles by asking ChatGPT and Grok what forums say about the codesEvidence: Described by poster
The poster reads codes with a scanner, then runs them through Google, ChatGPT and Grok, asking for the most likely causes based on online forums and reviews, and works through each likely fix with YouTube. They say the top-ranked fix has been right each time, and that they've fixed check-engine lights on three vehicles this way in two months: a Toyota 4.7 and Ford 6.0 and 7.3 engines.
ChatGPT, Grok · Personal · Source date:
- Replace a car sensor with Grok's help (it pointed the wrong way for 40 minutes)Recreated promptEvidence: Described by posterPartial
A driver replacing a sensor to clear a check engine light says Grok led them astray for 40 minutes; they had to use Google to find where the sensor was. Once they found it the job was easy, and the light went off. The poster's conclusion: AI is not good at fixing cars.
Grok · Personal · Source date:
- Trace a Mitsubishi engine light to a £100 oxygen sensor instead of a £2,500 catalytic converter with GrokRecreated promptEvidence: Described by poster
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.
Grok · Personal · Source date: