P0405 on GMC
Exhaust Gas Recirculation Sensor 'A' Circuit Low
P0405 on GMC vehicles indicates exhaust gas recirculation sensor 'a' circuit low. Au7o has documented this code across 1 GMC model — most commonly on Sierra 3500HD. P0405 is a generic OBD-II code meaning the engine computer detected an abnormally low voltage signal from the Exhaust Gas Recirculation (EGR) sensor 'A' circuit. This sensor reports the EGR valve's position or flow, which the computer uses to control exhaust gas recirculation for lowering emissions and combustion temperatures. A low signal indicates the reading is below the expected range, often due to a wiring or sensor fault. It mainly affects emissions and may cause light drivability issues but is not an immediate safety concern. Typical repair costs on GMC range from $900 to $2,800, depending on the specific model and root cause.
Common Causes of P0405
- •Faulty EGR position sensor (or DPFE sensor)
- •Open, shorted, or corroded EGR sensor wiring/connector
- •EGR valve stuck or carbon-clogged
- •Loss of reference voltage or ground to the sensor
- •Poor connector contact / pin corrosion
- •Damaged EGR valve assembly
- •PCM fault (rare)
P0405 on GMC by Model
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.
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View P0405 across all makes →Frequently Asked Questions
What does P0405 mean on GMC?▼
P0405 stands for "Exhaust Gas Recirculation Sensor 'A' Circuit Low." P0405 is a generic OBD-II code meaning the engine computer detected an abnormally low voltage signal from the Exhaust Gas Recirculation (EGR) sensor 'A' circuit. This sensor reports the EGR valve's position or flow, which the computer uses to control exhaust gas recirculation for lowering emissions and combustion temperatures. A low signal indicates the reading is below the expected range, often due to a wiring or sensor fault. It mainly affects emissions and may cause light drivability issues but is not an immediate safety concern. On GMC specifically, this code is documented across 1 model.
What causes P0405 on GMC vehicles?▼
Common causes on GMC: Faulty EGR position sensor (or DPFE sensor), Open, shorted, or corroded EGR sensor wiring/connector, EGR valve stuck or carbon-clogged, Loss of reference voltage or ground to the sensor, Poor connector contact / pin corrosion. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P0405 on a GMC?▼
Repair costs on GMC range from $900 to $2,800, depending on the specific model and root cause.
Which GMC models have P0405 documented?▼
Au7o has documented P0405 on 1 GMC model: Sierra 3500HD.