P1123
HondaThe Powertrain Control Module (PCM) has registered a condition where the Throttle Position Sensor (TPS) signal, while still within its nominal operational voltage range, consistently reports a throttle plate angle that is elevated beyond the PCM's calibrated expectations for the given engine load and airflow parameters.
Medium SeverityEssentially, the Engine Control Module (ECM) is receiving a reading from the Throttle Position Sensor that says the throttle is open more than it should be for how you're driving. This discrepancy can lead to the ECM miscalculating fuel delivery and ignition timing, affecting engine performance and drivability.
⚠️ Before You Begin (Safety First)
Ignoring a P1123 code isn't advisable. A misreporting Throttle Position Sensor can cause unpredictable throttle response, potentially leading to unintended acceleration or sudden power loss. Always ensure your diagnostic process is thorough to prevent unforeseen vehicle behavior. Disconnect the battery before working on electrical components to avoid short circuits and personal injury.
Common Symptoms
- Erratic engine idle speed, inconsistent with commanded RPM.
- Perceptible hesitation or surge during acceleration events.
- Reduced engine power, where the vehicle feels sluggish despite throttle input.
- Fuel economy degradation due to incorrect fuel trim adjustments.
- Check Engine Light illumination, indicating an emissions-related fault.
- Intermittent rough running conditions at various engine loads.
Common Causes
- Degradation or internal failure of the Throttle Position Sensor itself, leading to inaccurate voltage output.
- Intermittent short or open circuit within the TPS signal wire or reference voltage/ground circuits.
- Corrosion or poor contact at the TPS electrical connector, introducing resistance.
- Mechanical binding or wear in the throttle body mechanism, preventing smooth TPS operation.
- Less commonly, an internal Powertrain Control Module (PCM) processing error, although this is rare.
Frequently reported on: 2006-2011 Honda Civic, 2003-2007 Honda Accord, 2005-2009 Honda CR-V, 2005-2010 Honda Odyssey
Diagnostic Steps
- Connect an OBD-II scan tool capable of live data monitoring and observe the Throttle Position Sensor voltage (PID: TP or TPS_V) at various throttle angles, comparing it to specified values.
- Visually inspect the TPS wiring harness and connector for any signs of damage, fraying, or corrosion, ensuring secure connections.
- With the ignition on (engine off), slowly depress the accelerator pedal and observe the TPS voltage on the scan tool; it should rise smoothly without drops or spikes.
- Using a digital multimeter, backprobe the TPS connector to verify 5-volt reference, ground, and signal voltage integrity at the sensor itself.
- If the TPS signal voltage is erratic or consistently high even at idle, consider replacing the Throttle Position Sensor after verifying wiring and ground are pristine.
- Clear the diagnostic trouble code (DTC) and perform a test drive to confirm the repair, re-monitoring live TPS data.
👨🔧 When to Call a Professional
If your scan tool lacks the capability to graph TPS voltage against other sensor inputs like MAF or MAP, or if you're unable to logically deduce the root cause after voltage checks, it's prudent to involve a professional. A specialist can perform comprehensive drivability diagnostics, analyze live data streams, and verify the ECM's interpretation of sensor inputs to pinpoint the precise malfunction. Avoid simply replacing parts without a data-driven diagnosis.
Commonly Asked Questions
What specifically does 'in range but higher than expected' mean for the TPS?
It signifies that while the sensor isn't completely dead (out of range), its reported voltage for a given throttle plate position is consistently reading elevated. The ECM anticipates a specific voltage at idle or light throttle based on its internal maps, and if the TPS continuously provides a voltage higher than that calibrated threshold, it indicates a discrepancy in the actual versus perceived throttle angle.
Can a dirty throttle body cause a P1123 code?
Yes, indirectly. Carbon buildup around the throttle plate can prevent it from fully closing or seating correctly at idle. This physical obstruction would force the throttle plate to sit slightly more open, which in turn causes the Throttle Position Sensor to report a higher voltage than the ECM expects for a 'closed' throttle, thus triggering P1123.
Is recalibrating the TPS necessary after replacement?
On many Honda systems, the TPS is not user-adjustable or explicitly 'calibrated' in the traditional sense. The ECM usually learns the minimum and maximum throttle positions after a few drive cycles or an idle relearn procedure. However, always refer to the specific service information for your Honda model, as some integrated throttle bodies may require a specific factory scan tool procedure to properly reset learned values.
What is the impact on fuel economy?
When the ECM perceives the throttle is more open than it actually is, it will incorrectly enrich the fuel mixture. This 'false rich' condition means more fuel is injected than necessary for the actual airflow, directly leading to a decrease in fuel efficiency and potentially contributing to long-term fuel trim issues.