All Trucks, Campers, Trailers, RV's and Motor Homes - 2003 Honda Odyssey - No Heat

The heating system in my 2003 Odyssey does not heat the air. I have made the following observations, engine does not over heat, A/C operates normally (cools), defrost works, heater blower fan and the dashboard controls operate normally, there is no antifreeze loss or leaks, and both the upper and lower radiator hoses get hot to the touch. Additionally, the engine temperature gauge reading is lower than normal (75% of normal reading) and there is no/little pressure on the radiator. I would appreciate your comments.

I assume you mean the defroster blows air but no heat then I'd flush the cooling system there is no valving in the heater core temp is controled by a diverter.IF you have defroster heat and no cabin heat then a different diverter valve in the HVAC suitcase contols that. The little/no pressure does give me some worrys though that vehical should have 13 to 16 psi pressure in the cooling system you say its not getting hot but that indicates no flow in the cooling system which could be thermostat, low coolant, water pump,head gasket. Let me know what you find out.

To: Maniac Mechanic

Additional info, no defroster heat as well as no cabin heat, engine exhaust does not have antifreeze smell (head gasket issue), engine is not over heating (wouldn't this indicate water pump is OK?

Drove for about 20 minutes this morning and again noticed little or no radiator cap pressure with little or no boiling over when cap removed (antifreeze level up to radiator neck). Will replace radiator cap and then post finding. Thanks for the quick response.

Sounds to me like you have a thermostat that is stuck open.

Radiator cap was bad. Still no heat, will be replacing Thermostat next.

Replaced thermostat and antifreeze, still no heat! Is it possible for the waterpump to be bad and the engine not over heat? Any suggestions would be appreciated.

Rare but possible did you run some engine flush threw the system before putting the new a freeze in?I imagine you did since you went threw the trouble of replacing it. Last time I saw a vehicle do this and it be the pump was about a year ago on a late 90's jeep the impeller was full of holes causing the no/low flow situation for heat but it did run a little hot at the same time( slighty past center of the gauge) I hate to have you throw a pump at it and not fix it.I don't recall for sure but is there a bleeder screw in the cooling system on that one They look like a small bolt or screw usually on the thermo housing or the fitting on the block/intake going to the heater core if so get it up to temp and crack it open till the air bubbles stop and only steady coolant flow is visable after closing it back off. Then check if both lines going to and from the heater core get hot.If one side is hot and the other cold you have a plugged heater core if both sides are cold your still getting no flow and have an 95% chance that the pump is bad internally. Have the next two days off since we were very busy and allready racked up 23 hrs overtime will check back mid to late day tommarrow

Flushed and refilled with Honda Type II (recommended by Honda) antifreeze after replacing Thermostat. Current status after engine warm up, pressure present at Radiator cap, radiator upper and lower hoses hot, heater hoses hot and engine instrument panel temperature gauge reads about normal (about mid-gauge). Still no heat!

No bleeder screw on Thermostat housing, I will check further down line for a bleeder screw.

you have a bad diverter door actuator/sol now that you have done what you have and checked the other problems and repaired them if no bleeder screws this sol is located on the side of the HVAC suitcase and controls an internal door that diverts air flow from the ac evaporator and the heater core sorry for the long diag but those other problems had to be adderssed before the heater issue good luck

Where is the diverter door actuator/solenoid located (HVAC suitcase??)? Is there a test to determine if the diverter door actuator/solenoid is good? How difficult to remove? Look forward to your response.

Sorry about so late a response couldn't get the wife off the comp. The case is located under the dash slightly off center favoring the pass side the diverter door sol/actuator should be visable on that side also it will sit in a location between the area of the blower motor and where your heater core is.It will have a plug in or vac lines connecting it don't recall if that year was elect control or vac it will look like a small motor and is screwed into the case there may be a small linkage attached to it also remove it and try to set your temp to heat and see if it moves (hooked up of course) if not try and move the door where it hooked up to and see if you get heat. Now the tricky part if vac controlled check if you have vacume "switching" between the ports when changing from hot to cold if elect controlled check for voltage switching between the connection points on the plug. If the motor works the door itself is shot.If the motor doesn't work and the other tests fail then the problem is in your dash heater control panel wish I had better news for you but Good Luck