When Spark Plugs Fix the A/C

Working on modern vehicles can often feel like a love-hate relationship. While testing procedures and diagnostic tools have improved over the years, pinpointing the root cause of a problem has become more challenging, especially after certain shops have had their hands in the engine bay. That was exactly the case for one frustrated technician, who found himself trying to pinpoint a failure under the hood of a 2021 Toyota Tundra-ultimately leading to a quick call to ALLDATA's Tech Assist team.

The Toyota Tundra in question was experiencing A/C compressor issues. It would shut down or fail to engage altogether. The technician followed the factory diagnostic flowchart for B1422, Compressor Lock Sensor Circuit, and all signs pointed to a faulty A/C amplifier. But after replacing the amplifier, the issue remained. He then replaced the compressor, not once but twice, with no improvement. What initially seemed like a straightforward fix was quickly turning into a potential diagnostic nightmare.

The technician had followed the repair manual to a T, but something was still amiss, prompting a quick call to the ALLDATA Tech-Assist team. While on the phone, the Tech-Assist team member asked if any other codes were present. Stored in the history were the following:

• P0505 - Idle Control System Malfunction
• P050A - Cold Start Idle Air Control System Performance
• P1605 - Rough Idling
• P2118 - Throttle Actuator Control Motor Current Range/Performance

According to the technician, these codes didn't seem to be affecting the truck's operation. It was running well, showed no idle issues, and overall performance seemed normal. However, whenever the codes were cleared, the technician mentioned they reappeared immediately, a major cause for alarm.

The Tech-Assist advisor first suggested checking the misfire counters, but no misfires were recorded. Next came the recommendation to scope the crank sensor, since the B1422 code monitors crankshaft position in relation to compressor load and engine idle. Unfortunately, the shop didn't have access to a scope. Instead, the advisor walked the technician through a few additional fundamental checks:

• Perform a smoke test on the intake
• Confirm idle control using the scan tool
• Check fuel pressure
• Consider performing a module reset

The technician followed up the next day with a surprising discovery. While performing these basic checks, he inspected the spark plugs and noticed they looked brand new. When he mentioned this to the vehicle owner, the customer revealed that the A/C issues had started after another shop replaced the spark plugs.

Upon removal, the technician found that the plugs were aftermarket units purchased from Amazon. He replaced them with OEM spark plugs, and immediately the A/C system began working properly. The B1422 code and the related throttle and idle control faults never returned.

The fix? Spark plugs

While it might sound unbelievable, this case highlights a critical lesson: Engine performance and ignition components can have unexpected effects on seemingly unrelated systems. Diagnosing these kinds of issues may require a blend of traditional, old-school methods and thoughtful analysis to identify likely causes. In this case, poor-quality aftermarket spark plugs disrupted idle and crankshaft signals just enough to trigger compressor logic faults, sending the technician down a long and costly diagnostic path.