Owner Uses AI to Get Jeep Through Smog Tests
A 1994 Jeep Cherokee failing California emissions tests was fixed with help from AI tools and a low-cost custom hardware setup.
Updated on Nov. 13, 2026 in Car Maintenance
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Muhammad Zulali used Claude and Codex to help his 1994 Jeep Cherokee pass California smog tests after it was failing due to excessive NOx at certain test speeds. The project relied on a hardware interface costing no more than $15 in parts.
Why it matters
The Jeep's main ECU was too old to accept reflashed firmware, so the fix required a workaround that let the AI read and adjust engine data directly. The approach shows a low-cost option for owners of older vehicles facing expensive emissions retesting in California.
The Chrysler SCI bus communicates at approximately 7,800 baud with inverted electrical signaling, and the interface connects to the 6-pin diagnostic plug through three wires. The Arduino Nano setup logged fault codes and controlled values such as fuel pressure during test drives at 25 mph and 50 mph.
The players
Muhammad Zulali
The owner and developer who built the hardware interface and released the xj-scanner project on GitHub under the GPLv3 license.
The details
Zulali used an Arduino Nano to connect the engine's Chrysler SCI bus to a laptop, with Claude identifying the bus's baud rate and signal inversion requirements. Codex injected and ran custom code inside a nearby EEPROM because the main ECU could not be reflashed.
Timeline
The article about the Jeep smog-test project was published on November 13, 2026.
Roadmap
Owner-built diagnostic tools for older vehicles are increasingly possible because inexpensive microcontrollers can now interface with legacy automotive buses like Chrysler's SCI. This project extends that trend by pairing those tools with AI assistance to diagnose and adjust emissions-related engine behavior.
Vehicle owners in California facing smog-test failures on older cars may face repeated retesting costs of nearly $100 each. This approach shows that low-cost diagnostic methods may help some owners troubleshoot before paying for further repairs.
The takeaway
Owners of older vehicles who face emissions problems may find that low-cost hardware and open-source tools offer diagnostic options before committing to costly repairs. Checking whether your state's smog rules allow such workarounds is a useful first step.
Further reading
Explore more about Car Maintenance for related repair and emissions topics.
More information
Review the code and documentation in the xj-scanner project repository on GitHub.
Source note: This article includes information reported by Tom's Hardware.
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Do you think California's smog testing rules are fair to older car owners?
