Cars: 47 real cases

Find a clogged catalytic converter on a road trip in Mexico with ChatGPT

Kevin and Ruth's vehicle, Igor, was losing power in a tiny town in Veracruz, Mexico, and the pollution air pump had started making odd whirring noises. Kevin input the vehicle statistics and symptoms into ChatGPT, which gave three possibilities: a clogged catalytic converter, the fuel pump or the MAP sensor. The fuel pressure read 40 psi and a swapped MAP sensor changed nothing, which left the converter. ChatGPT suggested removing the oxygen sensor in front of the converter so the exhaust could escape; the engine fired right up and ran normally. The mechanics hollowed out the converter instead of replacing it, the check engine light stayed on, and the bill was 1,700 pesos (about $98 US).

Find an $80 purge valve fix instead of a new catalytic converter with ChatGPT

A Ford Ranger owner with the 3.0L engine had small evap leak codes that turned into catalytic converter codes. After a full diagnosis, a shop said the truck needed a new cat and gas cap for 'an astronomical sum.' The owner asked ChatGPT, which said this era of the 3.0L is notorious for the problem and suggested a new purge canister valve. The part cost about $80, it turned out to be the issue all along, and the truck has run smoothly since. The forum thread is titled 'ChatGPT saved me 3K.'

Negotiate a hybrid SUV price by email with three dealers using Claude

Derek Croote wanted to replace a 2011 Subaru Forester with a hybrid SUV and asked Claude 3.5 Sonnet for a negotiation strategy. Claude pointed out that '10 vehicles available across 3 dealerships' was leverage, and suggested emailing each dealer for an out-the-door price, aiming for 3–5% below MSRP, settling the price before the trade-in, and buying near the end of the month. Croote emailed three dealers on a Wednesday night near month's end and negotiated for two days by email, text and phone. Croote says it saved over $4K on the out-the-door price, including $1,500 for the trade-in, more than expected.

Trace a check-engine code and a tank that won't fill to a stuck valve with Grok, and fix it for $120

Christopher Wipper's mechanic wanted $169 just to troubleshoot a check engine light. AutoZone's free OBD2 scanner gave code P0458 (purge control valve circuit low), and the car wouldn't take fuel: it backed up in the fill tube. With no YouTube videos for the problem, Wipper used Grok to troubleshoot step by step: the air drain case on top of the fill port was clear, but the canister close valve's solenoid was stuck closed. Wipper had the replacement part in hand in 20 minutes and fixed it for $120 in less than an hour.

Get out-the-door quotes from 25 dealerships at once with a ChatGPT list and message, and pay $7,000 less

Isaiah Crossman, a salesperson, started shopping a few days before the end of the month, when dealers chasing monthly targets are most motivated. After a test drive and a benchmark price from the nearest dealer, Crossman had ChatGPT list the 25 closest dealerships with links to their contact forms and draft one message: driven it, ready to buy, this spec and these colours, send your best out-the-door price. Sending it to all 25 took about 7 minutes. Over about 2 hours of calls across a few days, a general manager 40 minutes away made a same-day deal: $7,000 less than one dealer's earlier offer and $2,100 less than the next lowest.

Find a severed transmission cooler line from a roadside call with Grok, then work out a hose fix that held

Shan Newton was hauling a heavy load up a mountain when a huge cloud of white smoke appeared behind the truck and fluid leaked down the road. Knowing nothing about fixing cars, Newton described what they saw to Grok 4 by voice; it said the white smoke pointed to the transmission and where to look, and the transmission oil cooler line had completely severed. After a passer-by towed the truck 18 miles into town, the new hose wouldn't fit inside the factory-crimped metal pipe. Grok suggested a hose with a bigger inner diameter to fit over the pipe, estimated the pressure at 10–20 PSI and said metal hose clamps would be enough. The workaround worked, and Newton says the truck runs better than before.

Build a goodwill case with ChatGPT and get a €6,000 out-of-warranty engine replacement for free

Thomas Weilbach's car was out of warranty, and the dealership said the only long-term fix, a full engine replacement quoted at €6,000, would be paid out of pocket. Weilbach used ChatGPT in research mode to dig into the symptoms (oil consumption, juddering under load and limp mode), known problems with that engine, service bulletins and how others had handled similar cases, testing each possible cause against the symptoms. ChatGPT then helped turn it all into a clear, structured argument. Weilbach took the case to the dealership, and the manufacturer approved the full engine replacement under goodwill at no charge.

Spot low brake fluid behind recurring brake warning lights with ChatGPT after two garage visits

The brake warning lights on the poster's car kept coming on. A mechanic claimed to have fixed it, the lights came back, and on a second visit the garage said it couldn't work it out without a fault code. At home, the poster noticed the brake fluid was low, confirmed it with ChatGPT from a photo, bought fluid and topped it up, and says that fixed it.

Compare options for towing a car cross-country with your truck with ChatGPT

A Hacker News commenter needed to tow their daughter's car across the country behind their truck: trailer or dolly, what each costs, and whether the truck could handle the combined weight. After a couple of piecemeal questions they gave ChatGPT the whole picture in one prompt (car make, truck model, start and end points), and it came back with a report with comparison tables and calculated towing weights for the different options.

Learn what limp mode is at the roadside and get moving again with ChatGPT

On the way to work, the poster's car suddenly crawled at about 4 mph with the check-engine light blinking and other dashboard lights on. They pulled over and asked ChatGPT, which explained limp mode. The poster switched the car off and on again, and says it worked fine afterwards, saving a panicked call to a mechanic.

Stop a mechanic fitting the wrong-polarity car battery from one photo with ChatGPT

When a mechanic arrived with a new battery for the poster's family car, the poster photographed the battery code and asked ChatGPT. It flagged that the battery was left-hand polarity while the Tata Punch needs right-hand, said new terminals would be needed for that reason, listed risks such as cables not reaching, sparks and warranty claims being refused, and recommended a DIN44R right-hand battery. The poster told the mechanic to bring the correct one, and the mechanic agreed to.

Fix check-engine lights on three vehicles by asking ChatGPT and Grok what forums say about the codes

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.

Replace a car sensor with Grok's help (it pointed the wrong way for 40 minutes)

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.

Help a locked-out Tesla owner get back in with Grok and Tesla support

At a Supercharger, a Tesla driver saw the owner of the car next to them locked out with their wallet and key inside and the charger connected. They asked Grok what to do; it recommended calling customer support, and they say they asked Grok to go ahead and call. After verifying the owner's identity and VIN, Tesla's agent opened the car door.

Win a lemon-law buyback of a 2025 Hyundai Elantra without a lawyer by following Grok (not Gemini)

A driver whose new 2025 Elantra's head unit failed (no CarPlay, broken navigation and Bluetooth) ran their whole lemon-law fight through Grok. After three dealer visits, the last a refusal to touch the car, Gemini advised waiting before sending the lemon-law letter; Grok said to lock the mileage, film the refusal, mail the letter and file with the state AG the same day, and they followed Grok. When the AG and Hyundai turned them down, Grok pushed them to file with BBB AUTO LINE and wrote a line-by-line rebuttal. They say the arbitrator ordered a repurchase in August and their loan was paid off to $0.00 in September.

Check a dealership's maintenance list for upsells with Gemini

At their car dealership for regular maintenance, a poster asked Gemini which of the suggested items were really necessary. They say 5 of the 6 items were unnecessary routine upsells or significantly overpriced, Gemini suggested where to go for the overpriced ones, and they only went with the ACV1 service, saving $2000.

Negotiate a car lease by pasting every dealer message into ChatGPT

A poster says they used ChatGPT for an entire car negotiation: they pasted whatever the dealer sent into ChatGPT, asked what they should pay, and sent back the replies it wrote, including every counteroffer. They say it saved them around $250 a month on the lease and was better informed than they were on local pricing, incentives and lease terms.

Get repair help from Gemini on an old Mitsubishi Triton and catch three wrong instructions

While replacing the balance shaft chain guides on an old Mitsubishi Triton, Hacker News user smackeyacky asked Gemini for help. It suggested removing the balance shaft chain as an emergency fix, though the chain also drives the oil pump; it suggested clearing water-contaminated oil by filling the crankcase with hot soapy water and running the engine; and its instructions for fitting the new gears left the chain guides misaligned. The poster ignored those steps and did it their own way.

Gemini vs ChatGPT on a check-engine EVAP code: replace the sensor or clear the code?

After a check-engine light on their 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. The driver cleared them, and after a long trip the code hadn't returned, avoiding a costly, labour-heavy part replacement for now.

Catch a 2-litre engine-oil overcharge on a car service bill with ChatGPT

Billed for a 6-litre pack of engine oil after a service on a Mahindra XUV 3XO at an authorised dealership, Gurpreet Singh Sodhi photographed the invoice and uploaded it to ChatGPT. It helped explain the invoice, identify the exact engine and its documentation, and prepare questions for the dealership. The dealership investigated, admitted the error, apologised and is re-issuing the invoice for 4 litres; the corrected bill is almost ₹1,500 lower.

Check a $930 dealership service estimate against warranty documents with Grok

In an interview summary, a truck owner said they'd been quoted $930 at the dealership for spark plug replacement. Before approving it, they uploaded their warranty and maintenance PDFs, the estimate and a screenshot and asked AI, 'Is any of this already covered under my warranty?' It found the work was already included in their prepaid maintenance package, saving $930. The interviewee's own post names Grok as the tool.

Skip a likely upsell on a Jeep's $1,800 service estimate after checking it with ChatGPT

At a Jeep dealership for a broken soft top, TikTok creator Debra was quoted $1,800 for an 80,000-mile service when they expected about $1,000. They asked for a printout, went outside and talked it through with ChatGPT, which told them the rear differential service was probably an upsell unless they towed heavy loads. They say skipping it saved $400. Motor1 notes the service is generally recommended every 30,000–60,000 miles and that experts say delaying it could cause problems later.

Repair a collision-damaged Honda Civic for under $1,000 instead of $10,000+ with Gemini as a mentor

After a collision left their daughter's 2019 Honda Civic with a $10,000+ shop quote and no collision coverage, a father spent weeks of evenings working with Gemini using photos, sensor data and questions. They say it helped them find a single crushed solenoid instead of a $4,000 transmission replacement, and guided which parts to buy and how to rebuild the front end. They report a DIY total under $1,000 and the car running smoothly at 70+ mph.

Track down a 1996 Volvo's stalling to a $35 fuel pump relay with Gemini

A driver whose 1996 Volvo kept stalling, and whose two mechanics couldn't pin down why, spent about 15 minutes going back and forth with Gemini. It suggested a failed or failing fuel pump relay that acts up when the car isn't warmed up. They say the part cost $35 on eBay and plugs in with only a screwdriver needed to open a compartment.