Diesel Trouble Codes

P0046 — Turbocharger/Supercharger Boost Control A Circuit Range/Performance — LLY / LBZ / LMM Duramax

P0046 on LLY/LBZ/LMM Duramax indicates the ECM sees the VGT boost-control circuit operating outside its expected range/performance. On this platform the…

Updated October 15, 2026

What it means

Generic OBD-II definition: the turbo boost control (VGT solenoid) circuit is not performing as expected. On LLY/LBZ/LMM the VGT is hydraulic with an ECM-controlled VGT control solenoid metering engine oil to the vane piston and a vane position sensor reporting position. P0046 is a circuit range/performance fault for that control path.1

Most likely causes

  1. VGT control solenoid electrical fault or degraded performance — The ECM-controlled VGT solenoid meters oil to the vane actuator. An intermittent open, high resistance, connector corrosion, or a solenoid that is electrically weak can cause the circuit to be out of range/performance. On this platform P0045 is the circuit/open code for the same solenoid, showing the solenoid and its wiring/ECM driver are a known failure point.21
  2. Sticking/sooted VGT vanes or unison ring — Carbon buildup can cause the vanes to stick, so the actual vane position lags or differs from the commanded position, producing a range/performance mismatch. This is a common VGT failure mode on the Garrett GT3788VA and is linked to boost-control learning/position faults on this platform.13
  3. Low or aerated engine oil supply to the VGT actuator — The VGT actuator is oil-pressure operated. Restricted oil feed, clogged screens, or aerated oil from a failing pickup can reduce actuator authority, leading to position errors reported as range/performance. Low/aerated oil is a documented contributor to VGT control faults on LLY/LBZ/LMM.13
  4. Vane position sensor signal out of range or poor tracking — The vane position sensor provides feedback to the ECM. A sensor drifting out of range, wiring chafing, or connector issues can make the reported position disagree with command, setting a boost-control range/performance code. P2563/P2564 are the position-sensor range/performance codes for this turbo.41
  5. Wiring/connector issues in the VGT control circuit — Chafed or corroded wiring and poor grounds between the ECM, VGT solenoid, and vane position sensor can cause intermittent voltage/resistance shifts that the ECM interprets as range/performance. Circuit integrity checks are standard for VGT solenoid faults on this platform.21

How to diagnose

  1. Verify freeze-frame and related codes. Note accompanying VGT codes such as P0045 (solenoid circuit/open), P003A (boost control position exceeded learning limit), P2563/P2564 (vane position sensor), P0234/P0299 (over/under boost). Related codes help separate electrical vs mechanical/hydraulic causes.
  2. Inspect VGT solenoid connector and wiring. Check for oil intrusion, corrosion, backed-out pins, and chafing along the harness to the ECM and turbo. Compare solenoid command vs actual behavior with a scan tool during a controlled idle-to-mid-load sweep, watching commanded vs actual vane position.
  3. Assess engine oil condition and supply to the VGT actuator. Verify oil level, quality, and absence of aeration; inspect the turbo oil feed restrictor/screen for restriction and check for excessive blow-by that can aerate oil. Low/aerated oil is a known cause of VGT control range/performance faults.
  4. Evaluate vane mechanical freedom and sensor feedback. With a scan tool, monitor desired vs actual vane position during a steady ramp. A slow or non-tracking actual position with good solenoid command suggests sticking/sooted vanes/unison ring or a failing position sensor. Do not manually force vanes; use scan data and indirect tests only.
  5. Check boost system integrity for contributing factors. Inspect intake boots, intercooler pipes, MAP sensor connector and wiring for leaks or signal issues that can influence boost control adaptation. A MAP signal out of range can interact with VGT control strategy.

Common mistake to avoid

Replacing the turbo before smoke-testing the intake. Boost leaks at intercooler boots, end tanks and clamps are a common cause of low power and underboost codes, and they mimic a failing turbo. Source: BD Diesel — 6.7L Power Stroke problems and real fixes.

Parts and tools you may need

Tools you’ll need

Rough cost and difficulty

Likely repairPartsShop laborWho usually does it
Wiring or connector repair$10–$1001–4 hrsDIY with tools and a manual
VGT actuator / vane control solenoid$100–$4000.5–2 hrsDIY with tools and a manual
Turbocharger$1,500–$3,5004–10 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 the VGT actuator or turbocharger requires removal, internal inspection, or cleaning of the unison ring/vanes, have a qualified diesel technician perform the work. Hot turbo and exhaust components pose burn and injury risks; improper service can cause engine damage. A professional can also perform ECM relearn procedures after repairs.

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) ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎

  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) ↩︎

Repair videos: P0046 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 Diesel Variable Turbo Intermittent Issues | P0046, P2563 — Watch Wes Work · 234K views

P0046 CODE TURBO BOOST CONTROL SOLENOID DURAMAX LLY LBZ LMM GMC Sierra Chevy Silverado How to fix — Whiplash TV · 40K views

2005 Chevy Duramax (P0046 and P2563) — wyattoneable · 37K views