Diesel Trouble Codes

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

Diagnostic reference for LLY/LBZ/LMM Duramax 2004.5–2010 with code P2564.

Updated October 15, 2026

What it means

The ECM sees the turbo boost control (vane) position sensor signal voltage below its valid range. On LLY/LBZ/LMM the Garrett GT3788VA vanes are moved hydraulically by engine oil pressure metered by the ECM-controlled VGT control solenoid, and a vane position sensor reports position back to the ECM. Circuit low usually means a failed vane position sensor, an open or shorted signal/reference wire, or a connector fault at the turbo.1

Most likely causes

  1. Failed vane position sensor (internal short/open) pulling signal low — The vane position sensor mounts on the Garrett GT3788VA turbo and is serviceable separately. An internal failure can bias the signal voltage below the ECM’s valid range.1
  2. Open or short-to-ground in the vane position sensor signal or reference circuit — Wiring damage, chafing near the turbo, or corrosion at the turbo connector can pull the signal low or open the reference, causing a circuit-low reading.1
  3. Connector fault / poor terminal contact at the turbo vane position sensor — Heat and oil exposure at the turbo can degrade the sensor connector, leading to intermittent or persistent low voltage.1
  4. ECM driver/reference supply issue affecting the sensor circuit — A low reference voltage or internal ECM fault can make the sensor appear low; verify supply/reference before condemning the sensor.1

How to diagnose

  1. Verify code and freeze frame; confirm P2564 is present and note engine oil temperature and run time.
  2. Inspect turbo vane position sensor connector at the Garrett GT3788VA for oil contamination, heat damage, bent terminals, and secure lock. Repair connector as needed.
  3. With key on engine off, check sensor reference voltage and ground at the sensor harness per service data; look for short to ground on signal wire.
  4. Monitor vane position sensor voltage with a scan tool while commanding VGT; a stuck low voltage indicates sensor or wiring fault.
  5. If voltage is present and within spec, perform a wiggle test on the harness from turbo to ECM while watching sensor PID for dropouts.
  6. If wiring and connector are good, replace the vane position sensor and clear codes; verify sensor voltage returns to normal range.

Parts and tools you may need

Tools you’ll need

Rough cost and difficulty

Likely repairPartsShop laborWho usually does it
Shop diagnosis—1–2 hrsShop
Wiring or connector repair$10–$1001–4 hrsDIY with tools and a manual
ECM/PCM replacement (programmed)$600–$2,0001–3 hrsShop

Typical US independent-shop figures; labor runs about $120–$180 per hour (dealers charge more). Confirm the diagnosis before buying parts.

When to see a pro

If wiring tests normal but the sensor voltage remains low, or if the VGT actuator requires removal, have a qualified diesel technician perform the repair. Do not attempt turbo or VGT actuator service without proper training and safety equipment.

Check for recalls

Recalls are tied to your truck’s VIN, so check yours directly: enter the VIN at NHTSA’s recall lookup. Open safety recalls are repaired free at a dealer.

Sources

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

Repair videos: P2564 on the LLY-LMM Duramax

Third-party videos, not ours — picked for this engine. Confirm anything against the factory service information for your truck.

Duramax turbo vane position sensor location, testing, and replacement — The Joy of Wrenching · 68K views

LBZ P2564 Vane Position Sensor Circuit Low Voltage FIX (New sensor did not fix the issue) — Ethan Anderson · 5K views