P0122: How to Diagnose & Fix — Throttle/Pedal Position Sensor/Switch 'A' Circuit Low Input

The electronic throttle module (ETM) on S40/V50 models with the 2.4L non-turbo (B5244S) engines can fail, setting throttle faults. The ETM controls the throttle blade electronically, and when it fails, the engine enters limp mode with severely limited power or refuses to rev above idle. Volvo's 10-year/200,000-mile Electronic Throttle System warranty extension applied to 1999-2002 P2/P80 models, not to the 2004+ S40/V50. The ETM failure is distinct from the P2 platform (older S60/V70) ETM issue but has similar symptoms.

First-generation Terrains (2010-2017) are prone to a sudden 'Reduced Engine Power' warning caused by a failing electronic throttle body. Carbon and grime build up inside the bore and the internal throttle position sensor (TPS) fails or reads erratically, causing the ECM to enter a limp/reduced-power mode that limits the vehicle to very low speed. This is a widely reported failure on the naturally aspirated 2.4L four-cylinder and 3.6L V6 engines and frequently appears alongside a 'Service StabiliTrak' message. The most commonly cited trouble code is P2135 (throttle/pedal position sensor voltage correlation). No NHTSA recall covers the throttle body; it is addressed through non-recall repair.

The 2001-2002 S60 (and other P2 platform Volvos) is notorious for ETM failure due to a design flaw in the throttle body electronics. The module develops internal solder joint cracks and corroded contacts, causing the car to enter limp mode, stall at idle, or refuse to accelerate. Volvo issued an extended warranty covering ETMs up to 10 years/200,000 miles on the 2001 S60 and the non-turbo 2002 S60, but many are now beyond that coverage.

The throttle-body-mounted TPS wears and produces an erratic voltage signal, causing high/hunting idle, stalling at stops, hesitation or bucking on acceleration, and — on automatics — erratic or harsh shifting. It is a very common TJ driveability complaint and often turns on the check-engine light.

Impalas frequently throw a cluster of warnings at once — 'Engine Power Reduced,' 'Service StabiliTrak,' and 'Service Traction Control' — that are usually one underlying drive-by-wire fault rather than three separate failures. The most common root cause is the electronic throttle body actuator (or the dual throttle-position sensors inside it) going out of range; the accelerator pedal position sensors can also disagree. Because the ECM cross-checks these dual sensors, any disagreement forces the car into limp-home mode with drastically reduced power. Carbon buildup on the throttle plate aggravates it, especially in cold weather.