OBD-II trouble code
P0120: Throttle/Pedal Position Sensor/Switch "A" Circuit
SAE J2012 names throttle or pedal position sensor A circuit. The standard's own example says a manufacturer may store this generic code, or the low code, or the high code, for the same stuck voltage.
Quick facts
- System
- Powertrain
- Category
- Throttle / Idle
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $150 – $950
- DIY difficulty
- Intermediate DIY
Browse every code in P0100–P0199, or start from the full code library.
What does P0120 mean?
P0120 is Throttle/Pedal Position Sensor/Switch "A" Circuit in SAE J2012 APR2002. Malfunction is not part of that line. Section 6 uses this sensor as the example of manufacturer choice. A 5-volt throttle-position input stuck near 0 volts may be stored as P0120 or as P0122. The same input stuck near 5 volts may be stored as P0120 or as P0123. An idle signal stuck at 1.5 volts when the calibration expected 1.0 volt may be stored as P0120 or as the range code P0121. The standard says the root cause is found in the diagnostic procedure and is not implied by which of those messages was chosen. The 1.0-volt and 1.5-volt figures are that example, not a specification for every vehicle.
GM's 2008 GRP09 sheet describes P0120 as a continuous or intermittent short or open in throttle-position sensor 1. The extracted threshold cell is shared with the coolant-temperature high test and reads as a window with 0.325 volt and 4.75 volts. The dedicated P0122 row on the same sheet is throttle position under 0.325 volt, and the P0123 row is over 4.75 volts, so the generic code on this sheet is the circuit test that covers both outsides of that window. Enables on the cell include ignition in unlock, accessory, run, or crank, system voltage over 5.23 volts, and no 5-volt reference codes. It is Type A. Those pin voltages are GRP09, for the 2.9L LLV, 3.7L LLR, and 4.2L LL8 vehicles in the 2008 grouping matrix.
The 1999 Ford PCED section 4 list does not include P0120. Low is P0122, a PID under 3.42 percent (0.17 volt). High is P0123, a PID over 93 percent (4.65 volts). Using the SAE example's 1.0-volt idle, or the GRP09 0.325-volt and 4.75-volt window, on that Ford PID will not match the test.
If the pedal no longer changes engine speed, stop driving and test the circuit with the vehicle parked. Do not move an electronic throttle plate by hand with the ignition on. The actuator is powered in run, and forcing the plate loads the geartrain. The Ford performance test that is in the same family is a key-on engine-running self-test at idle, not a hand sweep of the plate.
Common causes
- On GRP09, a short or an open in throttle-position sensor 1 that takes the signal under 0.325 volt or over 4.75 volts
- A 5-volt reference fault, which the GRP09 enable says must not already be stored as its own code
- On the 1999 Ford PCED, the causes printed under P0122 or P0123, because that manual does not list P0120: an open signal, an open reference, a short to ground, a short to power, an open signal return, a sensor not seated, a damaged sensor, or a damaged PCM
- A connector fault found with the sensor unplugged and the ignition on, measuring the reference pin rather than the signal pin
- A cable-throttle linkage or a sensor adjustment, which the SAE example allows as a cause of the 1.5-volt-versus-1.0-volt case and which does not apply to a motor-driven plate
Symptoms
- Malfunction indicator lamp with P0120
- On GRP09, sensor 1 outside 0.325–4.75 volts with system voltage over 5.23 volts and no reference code stored
- On a Ford from the 1999 PCED, no P0120 definition, and a low or high PID at 0.17 volt or 4.65 volts only if those codes are the ones stored
- Pedal travel that does not change the throttle-position parameter, checked with the vehicle parked
- The SAE example's stuck-at-1.5-volts idle, only as the standard's illustration of a range fault a manufacturer might file here
Diagnostic steps
- 1.Read which code the service information actually defines. If the book uses P0122 and P0123 and never defines P0120, follow those procedures. The 1999 Ford PCED is in that group. GRP09 defines all three.
- 2.Park the vehicle. If the pedal does not change rpm, do not continue a road test. Ignition on, engine off, watch sensor A. On GRP09, under 0.325 volt or over 4.75 volts is the out-of-range circuit result, with system voltage over 5.23 volts.
- 3.Key off, unplug the sensor, key on. Measure the reference pin to ground, not the signal pin. An open signal pin only shows the module's bias and does not prove the reference. GRP09 wants the reference codes absent before this test is believed. The Ford low-code causes include an open reference, and the Ford aides want you on the voltage PID.
- 4.Do not open the throttle plate by hand on a motor-driven throttle with the ignition on. For a cable throttle, the SAE example allows a binding linkage or an adjustment to explain an in-range voltage that is wrong at idle, and that check is done with the ignition off. For the Ford range code, the published check is a key-on engine-running self-test at idle after a stop, not a hand sweep.
- 5.A signal that stays out of the GRP09 window with a good reference and a good return is the sensor, or the throttle body when the sensor is not serviced separately. The diagram says which part is replaceable. A signal that is out of range with the sensor unplugged is the wire.
- 6.Clear the code and confirm, in park, that sensor A stays inside the window from closed throttle to the pedal applied, or inside the Ford percent limits if that is the chart you used. Record a road check. Do not watch the scan tool while driving.
Repair cost
$150 – $950
A separate throttle-position sensor is about $150 to $260 installed. When the sensor is not serviced separately, the throttle body is about $450 to $950.
Estimate your repair
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Open the Repair Cost Estimator with throttle body cleaning preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.