Diesel Trouble Codes

P2564 — Turbocharger Boost Control Position Sensor Circuit Low (LLY / LBZ / LMM Duramax)

P2564 on LLY/LBZ/LMM Duramax means the ECM is seeing an abnormally low voltage from the VGT turbocharger boost control position sensor circuit. The VGT on…

Updated September 2, 2026

What it means

On LLY/LBZ/LMM (2004.5–2010) the turbo is a variable-geometry Garrett VGT with an electric servo and position feedback sensor. P2564 is Turbocharger Boost Control Position Sensor Circuit Low per SAE J2012/GM enhanced. The ECM has detected an abnormally low voltage signal from the turbocharger boost control position sensor circuit. This code applies to LLY/LBZ/LMM Duramax 2004.5-2010 with VGT turbo and position feedback sensor.1

Most likely causes

  1. VGT position sensor internal failure / worn sensor element — The position feedback potentiometer inside the VGT actuator can wear or fail, pulling the signal low. This is a common electrical fault for P2564 on the LLY/LBZ/LMM VGT system.12
  2. Wiring harness chafing / corrosion at VGT actuator connector — The VGT actuator harness runs in a hot, oily engine bay. Chafing, oil contamination, or connector pin corrosion can create a short-to-ground or high resistance that drives the position sensor voltage low.13
  3. VGT actuator servo/electrical connector loose or oil-contaminated — Loose or oil-soaked actuator connector causes intermittent low voltage readings from the position sensor circuit.13
  4. ECM signal reference/ground issue affecting VGT sensor circuit — A shared 5 V reference or sensor ground problem can bias the position sensor low. Diagnose reference/ground integrity before condemning the turbo.12
  5. VGT mechanism sticking / vanes coked causing actuator over-travel and sensor fault — Severe soot/coking can cause the VGT vanes to stick, forcing the servo to an extreme position and triggering a range/performance or low circuit fault alongside P2564.24
  6. Aftermarket tuning / wiring modifications affecting VGT control — Non-factory calibrations or spliced wiring for VGT control can alter sensor voltage thresholds and set P2564.1

How to diagnose

  1. Verify code and freeze frame; confirm P2564 is present on LLY/LBZ/LMM with VGT.
  2. Inspect VGT actuator and wiring for heat/oil damage, chafing, and connector condition at the turbo.
  3. Check VGT position sensor supply/reference voltage and ground at the actuator connector per service info; look for short-to-ground or low reference.
  4. Monitor live VGT position sensor voltage/PID with scan tool during key-on and engine run; compare to expected range and sweep.
  5. Inspect turbocharger vane movement for binding/coking and actuator mechanical integrity; excessive resistance can contribute to sensor range faults.
  6. If electrical tests pass, evaluate ECM reference/ground circuits and consider actuator/sensor replacement as a unit on these VGT systems.

Parts and tools you may need

Rough cost and difficulty

Parts and labor vary by sub-engine and shop. VGT actuator replacement is common for persistent P2564 on LLY/LBZ/LMM. Electrical diagnosis can be low cost if wiring is the root cause.

When to see a pro

If bi-directional VGT tests are inconclusive, or turbo removal/inspection is needed, have a Duramax-experienced diesel technician perform electrical verification and actuator evaluation. Do not attempt high-pressure fuel or turbocharger disassembly without proper training and safety controls.

Sources

  1. Curated DTC seed — LLY / LBZ / LMM Duramax (curated) ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎

  2. Curated DTC seed — LLY / LBZ / LMM Duramax (curated) ↩︎ ↩︎ ↩︎

  3. Curated DTC seed — LLY / LBZ / LMM Duramax (curated) ↩︎ ↩︎

  4. Curated DTC seed — LLY / LBZ / LMM Duramax (curated) ↩︎