P2123 on 2007-2013 Chevrolet Avalanche: Reduced Power, Causes, and Fixes

What's Unique About the 2007-2013 Chevrolet AVALANCHE

The 2007-2013 Avalanche is built on the GMT900 platform, shared with the Silverado, Sierra, Tahoe, and Suburban of the era. A key issue across this platform, as documented in GM Technical Service Bulletin #PIP3783D, is poor electrical terminal tension at the accelerator pedal connector. This can cause intermittent high-voltage signals and trigger this code even if the pedal sensor itself is fine. Another related TSB for these platforms, #07-06-04-019D, points to water intrusion into the instrument panel-to-body harness connector in the driver's footwell as a cause for APP sensor correlation codes like P2138, which often appears with P2123.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this vehicle.

Symptoms You May Notice

• "Reduced Engine Power" message on the dashboard.
• Check Engine Light (Malfunction Indicator Lamp) is on.
• Poor or no acceleration; vehicle feels sluggish or 'lazy'.
• Vehicle may not accelerate past a certain low speed or RPM.
• Stabilitrak warning light may also illuminate.

Most Likely Causes

1. Failed Accelerator Pedal Position (APP) Sensor Assembly 🔴 High Probability → Shop Accelerator Pedal Assembly The electronic sensor is integrated into the pedal assembly and is a common failure point over time due to wear. Many owners on forums for GMT900 trucks report that replacing the pedal assembly is the ultimate fix after checking connections.
   How to confirm: Using a scan tool with live data, monitor the voltage for APP Sensor 1. If the voltage is stuck high (e.g., above 4.7V) and doesn't change when you press the pedal, the sensor has likely failed. You can also test the sensor's internal resistance with a multimeter.
   Typical fix: Replace the entire accelerator pedal assembly. The sensor is not sold separately. No programming is required after installation.
   Est. part cost: $60-$150
2. Poor Terminal Tension or Corrosion at APP Sensor Connector 🟡 Medium Probability This is a known issue specifically cited by GM in TSB #PIP3783D for this vehicle platform. The female terminals in the 6-pin connector can loosen over time, causing a poor connection. Water intrusion in the driver's footwell area can also lead to corrosion in this connector or the main body harness connector.
   How to confirm: Visually inspect the electrical connector at the accelerator pedal. Wiggle the connector while monitoring live data to see if the voltage reading changes. Check for any backed-out pins, corrosion, or signs of water intrusion. A technician video for the related P2138 code shows applying dielectric grease as a preventative measure.
   Typical fix: Clean the connector terminals and apply dielectric grease. If terminal tension is poor, the terminals may need to be carefully re-tensioned or the connector pigtail replaced.
   Est. part cost: $15-$40 for a new pigtail connector.
3. Damaged Wiring Harness ⚪ Low Probability Wires can chafe against sharp edges under the dash or break from repeated stress. A specific forum post for a similar GM vehicle with P2123 identified a broken ground wire (Brown wire) just inside the firewall as the culprit.
   How to confirm: Perform a continuity and resistance test on the signal (Dark Blue wire), reference, and ground wires between the APP sensor connector and the ECM. A visual inspection of the harness from the pedal towards the firewall is recommended.
   Typical fix: Repair the broken or shorted wire. This may involve soldering in a new section of wire and protecting it with heat shrink tubing.
   Est. part cost: $5-$20 for wiring repair supplies.

Rare But Worth Checking

• Failed Powertrain Control Module (PCM): This is very rare. Before condemning the PCM, all other possibilities, especially wiring and sensor issues, must be exhaustively ruled out. A failed PCM will often present with multiple, unrelated fault codes. The ECM on these trucks is an E38 model.

Diagnosis Steps

1. Connect an OBD-II scanner and confirm P2123 is present. Note any other codes, especially P2138, P2122, or P2127.
2. Using the scanner's live data function, observe the voltage for 'APP Sensor 1'. With the key on and engine off, it should be at a low voltage at rest and increase smoothly as you press the pedal. A reading stuck above 4.7V confirms the high input fault.
3. Locate the accelerator pedal assembly inside the driver's footwell. Disconnect the 6-pin electrical connector.
4. Inspect the connector terminals on both the harness side and the pedal side for looseness, corrosion, or pushed-out pins. This is a critical step based on TSB #PIP3783D. Wiggle the harness while watching live data to check for intermittent connections.
5. If the connector looks good, use a multimeter to check for a 5V reference and a good ground at the harness connector. A forum user identified the ground wire as brown and the signal wire for sensor 1 as dark blue.
6. If the wiring and connector are confirmed to be good, the APP sensor assembly is the most likely culprit.
7. Replace the accelerator pedal assembly, which is typically held on by two 10mm bolts.
🎬 Watch: A quick walkthrough on replacing the accelerator pedal assembly.
8. After replacement, clear the codes and perform a test drive to ensure the issue is resolved. A pedal relearn procedure is not required for this part.

Parts You'll Likely Need

• Accelerator Pedal Assembly with Sensor (OEM #25832864) — This is the most frequent cause of P2123. The sensor is integrated into the pedal assembly and is not sold separately. This part number also replaces older numbers 15847349 and 15101848.
  Trusted brands: ACDelco (GM Genuine Parts), Dorman (p/n 699-105), Standard Motor Products
  OEM price range: $95-$160
  Aftermarket price range: $60-$100

Related Codes That Often Appear With This One

• P2138 — This code indicates a correlation error between APP Sensor 1 and APP Sensor 2. It's very common to see this code alongside P2123 because if one sensor is reporting a high voltage, it won't match the reading from the other sensor. GM has a specific TSB (#07-06-04-019D) that addresses P2138 caused by water intrusion.
• P2122 — This code is for 'APP Sensor 1 Circuit Low Input'. Seeing it with P2123 can indicate an intermittent wiring problem causing the voltage to swing from one extreme to the other, or a failing sensor that is fluctuating wildly.
• P2127 — This code is for 'APP Sensor 2 Circuit Low Input'. It may appear with P2123 if there are widespread wiring or connector issues affecting the entire pedal assembly.
• P2128 — This code is for 'APP Sensor 2 Circuit High Input'. It's less common to see with P2123, but could indicate a short to voltage affecting both sensor circuits.

Technical Service Bulletins (TSBs) & Recalls

• PIP3783D: Addresses multiple APP sensor codes (P2120, P2122, P2123, P2125, P2127, P2128, P2138) and directs technicians to inspect the circuit for poor terminal tension, often leading to a 'Reduced Engine Power' message.
• 07-06-04-019D: Addresses intermittent P2138 codes caused by water intrusion into the instrument panel (IP) to body harness connector, located in the left-hand kick panel area. This can be caused by leaks from A-pillar seals or sunroof drains.

Platform-Specific Known Issues

• A known issue documented in TSB #PIP3783D is 'poor terminal tension' in the accelerator pedal position sensor's electrical connector, which can cause this code without the pedal itself being faulty.
• A related issue documented in TSB #07-06-04-019D is water intrusion into the IP-to-body harness connector in the driver's footwell, which can cause APP sensor correlation codes like P2138.

Mechanic-Grade Diagnostic Values

• APP Sensor 1 Voltage (Live Data) — expected: A smooth sweep from approximately 0.46V (pedal released) to 4.75V (pedal fully depressed).. Failure: The voltage is stuck high, above 4.75V, and does not respond to pedal movement.
• APP Sensor Potentiometer Resistance (End-to-End) — expected: Approximately 2.5 kOhms +/- 20%.. Failure: The resistance is substantially higher or lower than the specified range, or is an open circuit (infinite resistance).
• APP Sensor 1 Signal Resistance Sweep — expected: Starts at a higher resistance (e.g., 1.7 - 2.9 kOhms) with the pedal released, and smoothly decreases to a lower resistance (e.g., 1.6 kOhms or less) as the pedal is depressed.. Failure: The resistance value jumps, shows gaps, or stays stuck in one number as the pedal is moved.

Scan Tool Commands That Help

• Tech2 / GDS2: APP Sensor 1 and 2 Agree/Disagree Parameter — Use this to confirm if the two internal APP sensors are tracking each other correctly. The parameter should display 'Agree' while slowly and rapidly depressing the pedal. If it shows 'Disagree', it confirms a correlation fault between the sensors, often seen with code P2138.

Wiring & Ground Locations

• APP Sensor Connector (X109) — At the top of the accelerator pedal assembly in the driver's footwell.. This is the primary connection point. P2123 is for Sensor 1. Pin E (Dark Blue wire, Circuit 1161) is the APP Sensor 1 Signal. Pin F (White/Black wire, Circuit 1164) is the 5-Volt Reference for Sensor 1. Pin D (Brown wire, Circuit 1271) is the Low Reference (ground) for Sensor 1.
• ECM Connector (X1) — On the Engine Control Module (E38), which is typically located near the driver's side front wheel well.. This is the destination for the pedal signals. Pin 29 on the X1 connector receives the APP Sensor 1 Signal from the Dark Blue wire (Circuit 1161). Testing continuity between the pedal connector and this pin is crucial for diagnosing a wiring fault.
• G103 — A primary engine ground. Sources conflict slightly, with one stating it is on the front of the passenger side cylinder head, and another stating it is part of the main negative battery cable harness at the left front of the engine block. Technicians should inspect both locations.. While not the dedicated low-reference ground for the APP sensor, a poor connection at this major engine ground can introduce electrical noise and voltage offsets, potentially affecting sensitive sensor readings and causing intermittent faults that are hard to trace.
• G300 — A body ground located under the vehicle on a body mount, near the driver's side door area.. A forum user reported fixing recurring APP sensor codes by finding and cleaning a corroded frame ground under the driver's side door; G300 is the likely designation for this ground point. This highlights the importance of checking body and frame grounds, not just engine grounds.

When the Usual Fixes Don't Work

• In one documented case for a 2007 Silverado, the owner replaced both the throttle position sensor and the accelerator pedal sensor assembly, yet the vehicle continued to stall and set the pedal sensor code. This is a strong indicator that for some vehicles, the root cause is not the components themselves but a fault in the wiring harness (chafing, short, open) or a poor ground connection between the pedal and the ECM, which are often overlooked.

OEM Part Supersession History

• 15101848, 15847349 → 25832864 — GM regularly updates production and service parts to integrate new materials and technologies for improved reliability and performance.

Model Year Variations Within This Range

• 2007-2013: No significant variations have been identified for the APP sensor, its wiring, or the diagnostic approach for code P2123 within this generation. The GMT900 platform used the E38 ECM and a consistent wiring architecture for the accelerator pedal throughout these model years.