The '01 to '03 Duramax used the ECM grounds to control the coil of the IAH. For Federal Emissions applications, the IAH relay was housed together with the glow plug relay. California emissions applications had the IAH relay separate from the glow plug relay.
Cold Weather Start-Up Strategy
The '01 to '03 and '06-and-later versions of the engine have the intake air heater (IAH) and glow plug relays located in one assembly. Both relays have a power feed from a 175-amp fuse that is hot at all times. The ECM controls each relay independently and uses self-diagnostics related to the control of each function that includes diagnostic trouble codes. Fusible links provide circuit protection.
Both the IAH and glow plugs use different control circuitry on vehicles sold in California. These applications use a glow plug controller.
Cold weather start-ups are achieved at temperatures as low as minus 20 degrees F by the use of glow plugs in the combustion chambers. The initial glow plug heating time varies based on the system voltage and temperature. A lower temperature requires longer heating times. The ECM provides glow plug operation after starting a cold engine, which helps reduce white exhaust smoke and improves idle quality after starting up.
The coolant temperature sensor is a critical component on any electronically controlled engine. The ECM references this sensor to adjust fueling curves, glow plug operation, and even the transmission torque converter clutch application.
The '01 to '03 engine used the intake air heater (IAH) to warm the air entering the engine for proper combustion. The ECM operates the IAH to also reduce white smoke during warm-up and after long deceleration. The '04 and '05 models did not use an IAH. The IAH system returned for '06 but with modifications. The '06 LLY applications use a grid-style IAH controlled by the glow plug control module.
The following command logic was common to most applications when the IAH was called for.
Coolant temperature 50 to 104 degrees F
IAH commanded on 100% for 30 secondsIAH ramps down to 42% after 30 to 90 seconds of operationIAH will hold 42% for 90 to 500 secondsIAH will ramp to 0% after 500 to 600 seconds.
In 2007, LMM Duramax-equipped trucks received an exhaust temperature sensor to monitor the diesel particulate filter (DPF).
Coolant temperature below 41 degrees F
IAH commanded on 100% for 180 secondsIAH ramps down to 42% after 180 to 300 seconds of operationIAH will hold at 42% for 300 to 500 secondsIAH will ramp to 0% after 500 to 600 seconds
The LLY engine uses a glow plug system with a control module operated by the glow plug control module (GPCM). The GPCM connects to each of the eight glow plugs individually. This system uses silver-colored glow plugs that are marked LLY and are capable of providing 1,832-degree F heating within three seconds.
Coolant flow to the variable geometry turbocharger housing is controlled by a dedicated thermostat.
Glow PlugsAll Duramax engines use one glow plug per cylinder. The gold-colored LB7 glow plugs are 12-volt heaters that are energized prior to starting the engine, and they may also be operated for a short time after the engine has started (up to 30 seconds). The LLY, LBZ, and LMM engines use silver-colored glow plugs and operate on 4.7 volts.
To meet 2001 California emissions, a solid-state glow plug controller operated by the ECM had dominion over heating each cylinder separately.
During typical glow plug operation, 110-amp current is applied for 1.8 seconds, decreasing to the 30 amps that are necessary to keep the tip at 1,832 degrees F.
The silver (LLY) and gold (LB7) glow plugs can't be interchanged. Use of the gold glow plugs in place of the silver will result in hard starting due to a lack of heat. Using the silver glow plugs in place of the gold will cause possible failure to the glow plugs, cylinder head, and internal engine damage.