Coolant Loss From EGR Cooler Or DTC P2457 - keywords 6.6 6.6L cool cooling engine flow FOH fuel heat heater hose leak line LMM low odor operated over overheat pipe rear valve

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

A dealer may encounter a customer concern of coolant loss, coolant odor, or DTC P2457.

Normal diagnosis will lead to a leaking EGR cooler. The EGR cooler may have been replaced more than once.

If a dealer has encountered a leaking EGR cooler (may be repeat repair), DTC P2457, or a strong coolant odor, inspect for cooling system/heater system modifications. Modifications for a rear heater or a fuel operated heater (FOH) may cause poor flow (or no flow) through the EGR cooler. If coolant flow through the EGR cooler is restricted, the cooler can overheat. Overheating may induce an internal coolant leak from the EGR cooler. Verify the modifications made to the vehicle cooling/heater system have not restricted flow through the EGR cooler.

Improper routing of coolant supply hoses may also induce EGR overheating. If the vehicle has been modified for rear heat or FOH, inspect for proper hose/line routing. It is important to note the difference between supply and return especially if an auxiliary coolant flow pump is utilized to aid in coolant circulation to the rear auxiliary heater core. Some vehicles (RPO code ENC) are equipped with coolant supply and return lines under the passenger side of the cab. These lines can also be swapped/misrouted due to the differences between the diesel or gasoline line positions. Verify the supply and return lines are in the proper positions.

1. For diesel engine equipped vehicles the outboard pipe (as viewed from the rear of the vehicle) is the supply of engine coolant to the rear auxiliary heater. The inboard pipe is the return of engine coolant from the rear auxiliary heater to the engine cooling system.
2. For gasoline engine equipped vehicles, the inboard pipe (as viewed from the rear of the vehicle) is the supply of engine coolant to the rear auxiliary heater. The outboard pipe is the return of engine coolant from the rear auxiliary heater to the engine cooling system.

Note: To aide in proper filling of the cooling system, please use the SI procedure for Cooling System Draining and Filling (Vac N Fill).

Note: Dealers should contact the GM upfitter (www.gmupfitter.com) for instructions on adding rear heaters and/or fuel operated heaters.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.