P0401 on GMC
Exhaust Gas Recirculation Flow Insufficient
P0401 on GMC vehicles indicates exhaust gas recirculation flow insufficient. Au7o has documented this code across 6 GMC models — most commonly on Acadia, Canyon, Sierra 2500HD. This code means the Exhaust Gas Recirculation (EGR) system is not flowing enough exhaust back into the engine. The EGR system recirculates a small amount of exhaust into the intake to lower combustion temperatures and reduce nitrogen oxide (NOx) emissions; the computer has determined the actual flow is below what it commanded. The most common reason is carbon buildup clogging the EGR valve or its passages. You may notice pinging/knocking, rough idle, or a check engine light, and the car will fail emissions testing. Typical repair costs on GMC range from $150 to $4,500, depending on the specific model and root cause.
Common Causes of P0401
- •Carbon buildup clogging the EGR valve or passages
- •Stuck or faulty EGR valve
- •Blocked or restricted EGR ports/tubes
- •Faulty EGR temperature or position sensor
- •Faulty DPFE/EGR pressure sensor (on applicable systems)
- •Vacuum leak or failed vacuum control (vacuum-operated EGR)
- •Wiring or connector problems at the EGR valve
P0401 on GMC by Model
GMC Acadia(1 issue)
- 9T65 9-Speed Transmission Harsh Shifts and Hesitation2017-2025
The second-generation Acadia (2017+) uses the GM 9T65 9-speed automatic transmission which shares known issues with the Chevrolet Traverse and Blazer. Common complaints include harsh 1-2 upshifts, hesitation between 5-15 mph, lurching on light throttle in stop-and-go traffic, and the transmission hunting between gears on hills. GM has released multiple TCM calibration updates. The transmission is extremely sensitive to fluid condition — extended intervals with aging Dexron HP fluid contribute significantly to shift quality degradation.
GMC Canyon(1 issue)
- 8L45 8-Speed Transmission Torque Converter Shudder2015-2025
The 2015+ Canyon with the 3.6L V6 uses the GM 8L45 8-speed automatic (smaller sibling of the 8L90 in full-size trucks) which suffers the same torque converter lock-up clutch shudder at light throttle between 25-50 mph. The clutch friction material degrades and contaminates the fluid. GM issued TSB 18-NA-355 and Customer Satisfaction Program 18302 extending coverage to 6 years/100,000 miles. The fix and fluid are identical to the Sierra 1500 8L90 procedure — Mobil 1 Synthetic LV ATF HP (GM 19417577). This is the same issue affecting the Chevrolet Colorado V6.
GMC Sierra 2500HD(1 issue)
- Front Axle Disconnect Actuator and IWE Hub Failure (4WD Engagement Issues)2011-2023
Sierra 2500HD 4WD trucks use a front axle disconnect system with an electronic actuator and Integrated Wheel End (IWE) hubs. The actuator motor and position sensor commonly fail between 80,000-120,000 miles, causing the 4WD system to not engage, to partially engage (binding and vibration), or to throw a 4WD Service warning. Heavy-duty truck use — particularly towing and off-road — accelerates actuator wear. The IWE hubs (vacuum-operated on some variants, electric on others) also fail, causing a grinding or clicking noise from the front axle in 2WD mode when the hub disengages incompletely.
GMC Sierra 3500HD(1 issue)
- EGR Cooler Failure and Coolant Contamination (Duramax LMM/LML)2008-2016
The exhaust gas recirculation cooler on 6.6L Duramax LMM and LML engines is prone to internal cracking, allowing coolant to enter the EGR system and combustion chamber. Owners experience white steam from the exhaust, unexplained coolant loss, and in severe cases hydrolocking. This is a well-documented failure mode covered under extended warranty campaigns and referenced in NHTSA complaint database for 2008–2016 model years.
GMC Terrain(1 issue)
- 6T40/6T45 6-Speed Transmission Shudder and Harsh Shifts2010-2017
The 2010-2017 Terrain uses the GM 6T40 (2.4L) and 6T45 (V6) 6-speed automatic transmissions, both of which suffer from torque converter shudder, harsh shifts, and solenoid failures. The shudder occurs at light throttle between 30-50 mph when the torque converter clutch locks up. Solenoid pack wear causes P0756, P0751, and P0776 transmission fault codes. The transmission is sensitive to fluid condition — the 6T40/6T45 was originally filled with Dexron VI, but older Dexron VI degrades faster than newer formulations.
GMC Yukon(1 issue)
- 8L90 8-Speed Torque Converter Shudder2015-2020
The 8L90 8-speed automatic transmission in 2015-2020 Yukon and Yukon XL suffers from widespread torque converter lock-up clutch shudder at light throttle between 25-50 mph. The clutch friction material degrades and contaminates the transmission fluid, causing the shudder to worsen over time. GM extended warranty coverage to 6 years/100,000 miles under Customer Satisfaction Program 18302. The fluid fix (Mobil 1 Synthetic LV ATF HP, GM 19417577) resolves early-stage cases; advanced cases require torque converter replacement. This is the same issue affecting all K2XX platform full-size GM SUVs and trucks.
Looking for P0401 on a different make?
View P0401 across all makes →Frequently Asked Questions
What does P0401 mean on GMC?▼
P0401 stands for "Exhaust Gas Recirculation Flow Insufficient." This code means the Exhaust Gas Recirculation (EGR) system is not flowing enough exhaust back into the engine. The EGR system recirculates a small amount of exhaust into the intake to lower combustion temperatures and reduce nitrogen oxide (NOx) emissions; the computer has determined the actual flow is below what it commanded. The most common reason is carbon buildup clogging the EGR valve or its passages. You may notice pinging/knocking, rough idle, or a check engine light, and the car will fail emissions testing. On GMC specifically, this code is documented across 6 models.
What causes P0401 on GMC vehicles?▼
Common causes on GMC: Carbon buildup clogging the EGR valve or passages, Stuck or faulty EGR valve, Blocked or restricted EGR ports/tubes, Faulty EGR temperature or position sensor, Faulty DPFE/EGR pressure sensor (on applicable systems). Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P0401 on a GMC?▼
Repair costs on GMC range from $150 to $4,500, depending on the specific model and root cause.
Which GMC models have P0401 documented?▼
Au7o has documented P0401 on 6 GMC models: Acadia, Canyon, Sierra 2500HD, Sierra 3500HD, Terrain, Yukon.