It was in the low 50s this morning so I turned on the "Auto" function and set the temp to 70 which usually warms the interior up. Only cool air blew from the vents. We recently replaced the "coolant flow control valve" and had to add some coolant at the time but I never follow up checked it so I'll do that this evening. Any other thing to look at when diagnosing a problem with no heat?
A coolant control valve can get stuck in a position that cuts off coolant flow through the heater core, so that can be a cause. The air mix door can get stuck in a position that cuts off air flow through the heater core, so that can be a cause. For people of typical flexibility, it isn't too hard to peek under the dash and see if the air mix door moves.
Thanks pal. This is my daughter's car and I've been driving it for the past few weeks. She just informed me that it's been doing this for years so I'm gonna guess it's probably not the flow control valve since it's been replaced twice in the last two years and once about 3 months ago. Gonna check the blend door.
also check the heater core lines going through the fire wall. Both should be warm, if coolant is circulating throughout the heater core. If both hoses are warm, I'd look at the blend doors. If one or both lines are cool to the touch; you have no coolant flow. At this point, you'll need to troubleshoot why coolant isn't flowing. Coolant bleed issue, control valve issue, clogged heater core, coolant pump issue. Good Luck....
Haven't been able to look at anything yet. Google AI tells me that another item to look at is a faulty thermostat. I don't always believe Google AI so I thought I'd ask y'all.
The engine coolant thermostat controls coolant flow into the radiator - up front. Your heater core is behind that loop, so you get heat even when that thermostat is closed. FWIW; the car would be overheating too if that thermostat is stuck closed - especially over the summer months. If your talking about the heater core, that's the coolant control valve that you already replaced. You still need to check it. That plastic valve can be easily jammed up by internal coolant debris. There isn't a filter on your cooling system...
In cold weather, a faulty thermostat that fails to close can impair your cabin heat performance, by making the engine take a long time to reach, or never reach, normal operating temperature. But if you have a scan tool and you can watch the coolant temperature and it's coming up to 85 or 90 ℃ in a reasonable time, then that's not the issue.
P0125 and P0128 are both codes that can be set if the ECM doesn't think the engine reached normal operating temperature soon enough, on two drives in a row. So yes, a thermostat sticking open might well be something you'd catch by seeing one or both of those codes.
Thanks guys. How do you check the coolant control valve for being stuck? F°WIW as I drove today it was 50° F outside temp. I set the Auto function with 72° interior temp (which turns on the A/C and sets the flow to the feet.) . I turned off A/C and got nothing but cool air. Then I cranked up the temp to "High" and set the flow to be in the dash (which turns off the Auto function.) Immediate warm air for about 3 seconds and then cool again for a minute or so. It would repeat this pattern all the while I drove. Warm air for a few seconds and then cool air for a minute or more . . . over and over. It's trying to give me heat but something is not allowing it.
The first thing you should do is check the coolant level in the radiator. Remove the cap on top of the radiator. The coolant level should be all the way up to the top. If coolant is not at the top, add coolant to fill it up. There have been many instances reported on this Gen 2 forum about no heat. Many times, the coolant level is low in the radiator.
