What Does P1229 Mean?
DTC P1229 indicates the throttle position sensor B (TPS-B or APP sensor 2) signal fell outside the acceptable voltage range during the PCM's Key-On Engine-Off (KOEO) self-test. This typically means the secondary throttle position or accelerator pedal position sensor is reading a voltage the PCM does not expect at idle or rest position. The PCM uses dual TPS signals for redundancy and fault detection, so this mismatch triggers a rationality concern.
Common Causes
35%
Faulty throttle position sensor B or accelerator pedal position sensor
25%
Worn or contaminated throttle body bore causing erratic signal
20%
Wiring issue (high resistance, loose connection) in TPS-B circuit
15%
Throttle body requiring cleaning or relearn procedure
5%
PCM reference voltage supply problem
Diagnostic Steps
1
With key on engine off, use a scan tool to monitor TPS-B voltage — it should read approximately 0.5-1.0V at closed throttle and increase smoothly with throttle opening.
2
Compare TPS-A and TPS-B voltages; they should track proportionally (one may be inverse of the other depending on the design). Look for any dead spots or voltage dropouts.
3
Back-probe the TPS-B connector and verify the 5V reference and ground circuits are within specification.
4
Clean the throttle body with appropriate cleaner and perform a throttle position relearn procedure per the manufacturer's service manual.
5
If the sensor is integrated into the throttle body, inspect the throttle body for mechanical binding or carbon buildup that could affect rest position.
Estimated Repair Cost
$50 - $400
Parts + labor, varies by vehicle and location
DTC P1229 indicates the throttle position sensor B (TPS-B or APP sensor 2) signal fell outside the acceptable voltage range during the PCM's Key-On Engine-Off (KOEO) self-test. This typically means the secondary throttle position or accelerator pedal position sensor is reading a voltage the PCM does...
The most common cause of P1229 (Throttle Position Sensor B Out Of Self Test Range) is: Faulty throttle position sensor B or accelerator pedal position sensor
Typical repair costs for P1229 range from $50 to $400, depending on the vehicle, location, and whether you do it yourself or go to a shop.
An out-of-range TPS-B signal can cause the PCM to enter reduced power mode (limp mode), limiting throttle response and top speed. While this is a protective measure, the reduced acceleration capability could be hazardous in situations requiring quick maneuvering.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P1229 to identify the root cause.
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Quick Info
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Powertrain
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Electronic Throttle Control
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