Poor Heat At Idle - keywords 9C1 9C3 coolant cooling core defrost enforcement engine floor flow heat heater hvac idle law mode no police poor performance vent

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

Poor heat at idle, however, if the engine RPMs are raised the concern no longer occurs.

Note: Be sure to follow all SI safety procedures and caution notices.

1. With the engine cooled off, remove the coolant pressure cap.
2. Remove upper heater core hose from the metal pipe on the engine.
3. Add coolant to the metal pipe, until full.
4. Raise the rubber portion of the heater core hose as high as it will go with it still attached at the heater core. Using a funnel, add coolant until the hose is full.
5. Reconnect the heater core hose.
6. Start engine, have assistant raise the RPMs to about 1500 to 1700 RPMs, top coolant off at engine, then before lowering engine RPMs, install the coolant pressure cap.
7. Fill coolant reservoir as necessary, then check the heat at idle.

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.