The part about the incorrect gear ration codes setting is only related to Land Rover’s. The MAF signal that’s causing this code to set does not have an obvious problem, the signal looks ok at a glance.
Take a look at the MAF signal graph display below. The best way to diagnosis these slight differences in MAF signal is with a scanner that has a good graph display. The signal voltage reads anywhere from 3.7-4.0 volts which is ok from my experience. Fuel pressure was within specifications (45-50 psi) and the MAF was reading correctly, I thought! I can hook up the scope and perform a snap throttle test. Then of course P0171 and P0174, lean both banks. The TCM (transmission control module) is setting incorrect gear ration codes which means the transmission is slipping (usually). The vehicle has no drivability concerns and was hard to diagnosis. Symptoms: NONE, Slight pre-detonation (pinging) when hot Vehicle: 2001 Land Rover Discover II Codes: P0171, P0174, TCM Incorrect Gear Ratio
Mass Air Flow Sensor Testing,P0171-P0174 System Lean
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