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I was able to use ISTA to read the temperature sensors by selecting the IHKA module, selecting "Call Up ECU functions", "Diagnosis scan" tab, "Status - IHKA high", then selecting whatever sensors I wanted to read. I confirmed that the L/R vent temperatures and cabin temperatures matched my IR thermometer.
I cranked up the temperature to max and went for a road test. Once the coolant temperature reached 82C things started to happen: fan speed ramped up (auto mode), L/R heater core temperatures rose, L/R vent temperatures rose, and then the interior temperature rose. All good so far.
I pulled over to watch the readings. Then things seemed to go wonky. One or both heater core temperatures would drop very quickly sometimes to as low as 5C, the vent temperatures would follow, then the IHKA would react by lowering the fan speed. In this state it wasn't putting out any heat even though it was cranked up to max and the cabin temperature was cooler than that.
AC on or off, recirc on/auto/off, etc. had no effect either way.
When I revved the engine, or got back on the road, I could sometimes get the heater core temperatures to climb again and the IHKA to add heat to the cabin. Ordinarily I might suspect that the higher water pump pressure from revving the engine was pushing more coolant past a dead secondary pump, but that secondary pump is only 1 year old, and it seems to work fine in rest mode.
Not sure where to go from here. I wish I could confirm the state of the heater control valve solenoids and the secondary water pump state.
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12-18-2024, 01:59 PM
Hybrid Mode
