Duramax Exhaust Gas Temperature Sensor Location by Engine
| Light color | Amber |
|---|---|
| Urgency | Service soon (amber) when an EGT sensor code is active |
| Safe to drive | Yes, but DPF regeneration may be inhibited with a failed sensor |
| Common cause | Sensor failure or wiring damage from heat; seized bung on high-mileage trucks |
| DIY or shop | Either - straightforward if bung is not seized |
The number of exhaust gas temperature (EGT) sensors on a Duramax 6.6L diesel depends entirely on which engine you have. The LMM (2007.5-2010) uses two sensors; the LML (2011-2016) and L5P (2017+) each use four. Every sensor threads into a bung welded to the exhaust pipe or aftertreatment housing, and each monitors a specific point in the DPF regeneration and emissions control system.
When one fails, the truck often triggers a HEST (High Exhaust System Temperature) warning or a DPF-related code before setting a specific EGT sensor fault. Knowing the exact location before you get under the truck saves a lot of time.
LMM (2007.5-2010) Sensor Positions
The LMM Duramax runs a two-sensor EGT system. Both sensors are on the driver side of the truck in the downpipe-to-DPF section of the exhaust:
- Position 1 (upstream / EGT1) - located on the downpipe roughly 8-10 inches downstream of the turbocharger outlet, before the diesel particulate filter (DPF). This sensor is the primary load monitor and feeds the regen control strategy.
- Position 2 (downstream / EGT2) - located after the DPF, monitoring outlet temperature to confirm the filter has regenerated properly and to protect the system from overtemperature events.
The LMM DPF assembly sits under the cab on the driver side frame rail. Both bungs are accessible from below without removing any major components, though working around the heat shield panels requires some patience. Common OEM part number across both positions is 12623113.
- High Exhaust System Temperature (HEST)Amber
- Meaning: Exhaust gas temperature has exceeded safe limits, often because a failed EGT sensor has allowed an uncontrolled DPF regeneration cycle to run too long.Recommended action: Pull over and let the exhaust cool before continuing. Do not park over dry grass or combustible materials while the HEST light is on.
LML (2011-2016) and L5P (2017+) Sensor Positions
Starting with the LML, GM added selective catalytic reduction (SCR) and urea injection (DEF system) to the Duramax aftertreatment package. This brought the sensor count to four, with each sensor bracketing one of the major aftertreatment components:
- Position 1 (EGT1) - on the downpipe approximately 8-10 inches downstream of the turbo outlet, upstream of the diesel oxidation catalyst (DOC). This is the hottest sensor in the system during regen and the one most commonly associated with wiring damage from radiant heat.
- Position 2 (EGT2) - between the DOC outlet and the SCR inlet. This sensor is on the mid-section of the aftertreatment housing, which on the LML and L5P is a single integrated unit bolted under the cab on the driver side.
- Position 3 (EGT3) - between the SCR outlet and the DPF inlet. It threads into the short connecting pipe between the two sections of the aftertreatment housing.
- Position 4 (EGT4) - at the rear of the DPF, angled slightly upward toward the driver side. This is the outlet temperature sensor and the one used to confirm a completed regen cycle.
The LML and L5P sensors use the same bayonet connector style and very similar part numbers to the LMM. The integrated aftertreatment housing location means all four sensors are accessible from below in roughly the same area - no need to drop the exhaust system completely for a single sensor swap.
For a parallel reference from the Ford side of diesel emissions systems, the 6.7 Power Stroke NOx sensor location guide covers a similar concept for that platform.
How to Find the Sensor You Need to Replace
The scan tool code identifies which position has failed. GM uses the following general naming conventions:
- P242F / P2459 - DPF regeneration frequency (sensor input feeds these)
- P0544 - EGT sensor 1 circuit (Position 1 failure)
- P0546 - EGT sensor 1 high (Position 1 overtemperature read or open circuit)
- P2031 - EGT sensor 2 circuit (Position 2 failure, after DPF on LMM)
- On LML/L5P, Positions 2, 3, and 4 each have corresponding P-codes in the P2031-P2034 range
Once you have the code, count from the turbo outlet back: Position 1 is always the first sensor downstream of the turbo. Count forward from there to find 2, 3, or 4.
If you are also dealing with an EGR-related fault alongside the EGT code, address the EGT sensor first since a missing exhaust temperature input can cause the PCM to over-fuel on regen attempts, which increases EGR soot loading.
Replacement Tips
The main obstacle on high-mileage trucks is a seized bung. Heat cycling welds the sensor threads into the bung over time, and forcing a seized sensor often pulls the bung out of the pipe. Before attempting removal:
- Soak the sensor base with a good penetrating oil (PB Blaster, Kroil) at least an hour before removal, and re-apply if the truck has sat. Heat from a propane torch on the pipe immediately surrounding the bung helps significantly.
- Break the sensor loose with a 22 mm sensor socket (not a standard socket - sensor sockets have a slot for the wiring pigtail). Turn counterclockwise; never use an impact gun on a stuck sensor.
- If the bung pulls anyway, Dorman sells an OE FIX kit (part 917-801) that replaces the bung with a repair fitting without requiring pipe replacement.
Replacement sensors are available from ACDelco (original supplier), Dorman, and Standard Motor Products. Install the new sensor with a small amount of anti-seize on the threads (avoid getting any on the sensor tip), and torque to 30-35 ft-lb. Reconnect the bayonet connector until it clicks, then clear the code and run a short highway drive to confirm no fault returns.
On the LML and L5P, clearing EGT codes often requires resetting the DPF learned values with a scan tool in addition to clearing the DTC. A generic reader may not have this capability - GM MDI or similar professional tool is preferred. This is similar to what you would encounter diagnosing a GM 5.3L P0307 misfire where a generic reader gets you part of the way but factory software finishes the job.
Frequently Asked Questions
Q: How many EGT sensors does my Duramax have?
A: Two on the LMM (2007.5-2010), and four on the LML (2011-2016) and L5P (2017+). The increase came with the addition of the DEF/SCR system in 2011, which required temperature monitoring at more points in the aftertreatment system.
Q: Can I drive with a bad EGT sensor?
A: In most cases yes, but with limitations. The PCM will often inhibit active DPF regeneration when an EGT sensor circuit is open or out of range, because it cannot safely monitor exhaust temperature during the regen burn. Extended driving with an inhibited regen leads to DPF loading, and a fully loaded DPF will eventually force a parked regen or set its own faults.
Q: What does the HEST warning light mean on a Duramax?
A: HEST stands for High Exhaust System Temperature. It illuminates when the exhaust temperature during a DPF regen cycle reaches a level that could ignite combustibles under or near the truck. It is normal to see it briefly during a highway regen. If it stays on or comes on repeatedly, check for EGT sensor faults that may be causing an uncontrolled regen.
Q: Are all four LML EGT sensors the same part?
A: They use the same connector type and similar thread pitch, and some positions share part numbers, but they are not all interchangeable. Positions 1 and 2 see higher peak temperatures than 3 and 4, and some part numbers reflect this with different internal calibrations. Order by position number from GM or check the specific part number for each bung location in your service manual.
Q: Do I need a scan tool reset after replacing an EGT sensor?
A: Yes, particularly on the LML and L5P. Clearing the DTC alone is not always enough - the PCM also stores learned DPF pressure and temperature values that may need a reset so the regen strategy recalibrates to the new sensor. A generic OBD-II reader can clear the code but may not reset the adaptive DPF data; GM MDI or a professional scan tool with GM-specific calibration is the cleaner approach.