P0121 Throttle Position Sensor/Switch A Circuit Range/Performance Problem

Description and meaning of DTC p0121

This diagnostic trouble code (DTC) is a generic powertrain code, which means that it applies to OBD-II equipped vehicles. Although generic, the specific repair steps may vary depending on make/model. The Throttle position sensor is a potentiometer that measures the amount ofthrottle opening. As the throttle is opened, the reading (measured in volts)goes up. The powertrain control module (PCM) supplies a 5 Volt reference signalto the throttle position sensor (TPS) and usually a ground also. A general measurementis: at idle = . 5 Volts full throttle = 4. 5 Volts. If the PCM detects that thethrottle angle is greater or less than it should be for a specific RPM, it willset this code.

p0121 diagnostic trouble code symptoms

Symptoms of a P0121 trouble code could include:Malfunction Indicator Lamp (MIL) illumination (Check Engine Light or ServiceEngine Soon light) Intermittent stumble on acceleration or deceleration Blows black smoke on accelerationNo start

DTC p0121 - possible causes

A code P0121 may mean that one or more of the following has happened:TPS has intermittent open or short internallyHarness is rubbing and causing an open or short in the wiring Bad connection at the TPS Bad PCM (less likely) Water or corrosion in connector or sensor

How to fix OBD-II diagnostic trouble code p0121

1. If you have access to a scan tool, see what the idle and WOT (wide openthrottle) readings are for the TPS. Check if they're close to the specificationsmentioned above. If not, then replace the TPS and re-check. 2. Check for an intermittent open or short in the TPS signal. To do that, youcan't use a scan tool. You'll need an oscilliscope. The reason is because scantools take samplings of many different readings over just one or two data linesand can miss an intermittent drop out. Hook up your oscilliscope and watch thesignal. It should sweep up and down smoothly with no drop outs or spikes. 3. If no problems were noticed, perform a wiggle test. Do this by wigglingthe connector and harness while watching the pattern. Does it drop out? If so,replace TPS and re-check. 4. If you have no TPS signal, check for 5 Volt reference at the connector. If it's present, check the ground circuit for open or shorts. 5. Make sure the signal circuit isn't 12V. It should never have battery voltage. If it does, trace circuit for short to voltage and repair. 6. Look for any water in the connector and replace TPS as necessary. Other TPS sensor and circuit related DTCs: P0120, P0122, P0123, P0124

More OBD-II diagnostic trouble codes (DTC)