P249D on GMC
Closed Loop Reductant Injection Control At Limit - Flow Too Low
P249D on GMC vehicles indicates closed loop reductant injection control at limit - flow too low. Au7o has documented this code across 1 GMC model — most commonly on Sierra 2500HD. Generic diesel SCR code indicating the closed-loop reductant (DEF) injection control has reached its adjustment limit because DEF flow is too low. The PCM is commanding more DEF than the system can deliver, so NOx cannot be adequately reduced. Typical repair costs on GMC range from $400 to $2,500, depending on the specific model and root cause.
Common Causes of P249D
- •Clogged or restricted DEF injector
- •Weak DEF supply/metering pump
- •Restricted DEF lines or filter
- •Low DEF level or poor DEF quality
- •Failing NOx sensor skewing the feedback loop
P249D on GMC by Model
GMC Sierra 2500HD(1 issue)
- LML DEF Tank Heater, DEF Injector and NOx Sensor Failures Triggering Speed-Limited Limp Mode2011-2016
The 2011-2016 6.6L Duramax RPO LML added selective catalytic reduction, and the aftertreatment hardware is the engine's most frequent expense. The DEF tank heater and level/quality sender assembly fails often, the DEF (reductant) injector crystallizes and clogs, and pre-2015 NOx sensors drift out of calibration and report false "DEF quality poor" faults. Because these are emissions-critical, the truck gives a countdown of remaining miles and then enforces a hard speed limit - typically 65 mph then 4 mph - regardless of whether the DEF fluid is actually bad. Owners on duramaxforum.com and silveradosierra.com report P20EE, P249D and P22FE as the recurring set. This is LML-specific; the LMM has no DEF system.
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View P249D across all makes →Frequently Asked Questions
What does P249D mean on GMC?▼
P249D stands for "Closed Loop Reductant Injection Control At Limit - Flow Too Low." Generic diesel SCR code indicating the closed-loop reductant (DEF) injection control has reached its adjustment limit because DEF flow is too low. The PCM is commanding more DEF than the system can deliver, so NOx cannot be adequately reduced. On GMC specifically, this code is documented across 1 model.
What causes P249D on GMC vehicles?▼
Common causes on GMC: Clogged or restricted DEF injector, Weak DEF supply/metering pump, Restricted DEF lines or filter, Low DEF level or poor DEF quality, Failing NOx sensor skewing the feedback loop. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P249D on a GMC?▼
Repair costs on GMC range from $400 to $2,500, depending on the specific model and root cause.
Which GMC models have P249D documented?▼
Au7o has documented P249D on 1 GMC model: Sierra 2500HD.