Poor Heater Performance Due to Coolant Hose Restriction

Poor heater performance may be experienced on some 2020 Silverado and Sierra models equipped with the 3.0L diesel engine (RPO LM2). The poor performance may be caused by the heater core inlet or outlet hoses becoming twisted or kinked, which may restrict coolant flow.

Use GDS2 to compare the heater core inlet temperature sensor 3 to the heater core outlet temperature sensor 4. When comparing the difference in the heater core temperature sensors, make sure the blower motor is on high with the HVAC temperature set to full hot.

If there is a hose restriction, there will be a significant difference between the temperatures; for example, the inlet temperature may be 147°F (64°C) and the outlet temper may be 82°F (28°C). Typically, the temperatures will be within 10–20°F (5.5–11°C).

Follow the appropriate Service Information for poor heater performance. If diagnostics do not lead to a correction, inspect the heater core inlet and/or outlet hoses for any twists or kinks.

In some cases, it may be difficult to see the twist or kink in the hose due to the conduit that covers the hoses.

In the following examples, the illustration showing the heater core inlet hose (Fig. 11, #1) and the heater core outlet hose (Fig. 11, #2) correlate to the actual vehicle photos of the inlet hose (Fig. 12, #1) and outlet hose. (Fig. 13, #2)

Fig. 11

Fig. 12

Fig. 13

– Thanks to Jim Will

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