Heater control valve - 2000 Mitsubishi Eclipse

Sounds like the cable is disconnected from the water valve. Check under hood at the fire wall where heater hoses connect to heater core. Water control valve should be in one of the two hoses and the cable end should be visible . Water is off when A/C is on.

It's a vacuum line to control the valve? It will connect there at valve and run into and under the dash to the back of the heater control panel. All the vacuum control hoses for the heat and AC are in a pod that connects to the back of the heater controls. A vacuum line from the engine is also there, the pod will send the vacuum signal out to various doors on the heater/AC case, as the controls demand. One also goes to the heater control valve.

Either your heater control valve is not properly operating or your heater core is clogged. Locate the heater control valve under the hood, should be close to firewall on heater hose, have someone adjust temperature from hot to cold and see if you can see the heater control valve operating if so replace the heater core, if its not doing anything replace it(heater control valve).

If it's not blowing out hot air, the blend door may be the problem on the 1990 Isuzu Trooper.

Heater Water Control Valve REMOVAL & INSTALLATION On early models the heater control valve was part of the heater core inlet. To replace the control valve, remove the heater core as outlined in this section. Remove the control valve from the heater core, being careful not to damage the core. Use new gaskets when installing new valves. The remainder of the vehicles are not equipped with heater water control valves. They use heater unit doors to regulate the amount of heat entering the vehicle. --- I would check that both tubes running to the heater core are getting hot. If they are, then there is a blend door problem. If both tubes are not getting hot, the heater core is blocked somewhere or the heater control valve, if so equipped, is in need of replacement. Good luck on this repair.

here are all poss causes of check engine light.
Generic Trouble Codes

P0001-P0099 – Fuel and Air Metering and Auxiliary Emission Controls
Code Description
P0001 Fuel Volume Regulator Control Circuit/Open
P0002 Fuel Volume Regulator Control Circuit Range/Performance
P0003 Fuel Volume Regulator Control Circuit Low
P0004 Fuel Volume Regulator Control Circuit High
P0005 Fuel Shutoff Valve Control Circuit/Open
P0006 Fuel Shutoff Valve Control Circuit Low
P0007 Fuel Shutoff Valve Control Circuit High
P0008 Engine Position System Performance (Bank 1)
P0009 Engine Position System Performance (Bank 2)
P0010 A Camshaft Position Actuator Circuit (Bank 1)
P0011 A Camshaft Position - Timing Over - Advanced or System Performance (Bank 1)
P0012 A Camshaft Position - Timing Over - Retarded (Bank 1)
P0013 B Camshaft Position - Actuator Circuit (Bank 1)
P0014 B Camshaft Position - Timing Over - Advanced or System Performance (Bank 1)
P0015 B Camshaft Position - Timing Over - Retarded (Bank 1)
P0016 Crankshaft Position - Camshaft Position Correlation (Bank 1 Sensor A)
P0017 Crankshaft Position - Camshaft Position Correlation (Bank 1 Sensor B)
P0018 Crankshaft Position - Camshaft Position Correlation (Bank 2 Sensor A)
P0019 Crankshaft Position - Camshaft Position Correlation (Bank 2 Sensor B)
P0020 A Camshaft Position Actuator Circuit (Bank 2)
P0021 A Camshaft Position - Timing Over - Advanced or System Performance (Bank 2)
P0022 A Camshaft Position - Timing Over-Retarded (Bank 2)
P0023 B Camshaft Position - Actuator Circuit (Bank 2)
P0024 B Camshaft Position - Timing Over - Advanced or System Performance (Bank 2)
P0025 B Camshaft Position - Timing Over - Retarded (Bank 2)
P0026 Intake Valve Control Solenoid Circuit Range/Performance (Bank 1)
P0027 Exhaust Valve Control Solenoid Circuit Range/Performance (Bank 1)
P0028 Intake Valve Control Solenoid Circuit Range/Performance (Bank 2)
P0029 Exhaust Valve Control Solenoid Circuit Range/Performance (Bank 2)
P0030 HO2S Heater Control Circuit (Bank 1 Sensor 1)
P0031 HO2S Heater Control Circuit Low (Bank 1 Sensor 1)
P0032 HO2S Heater Control Circuit High (Bank 1 Sensor 1)
P0033 Turbo Charger Bypass Valve Control Circuit
P0034 Turbo Charger Bypass Valve Control Circuit Low
P0035 Turbo Charger Bypass Valve Control Circuit High
P0036 HO2S Heater Control Circuit (Bank 1 Sensor 2)
P0037 HO2S Heater Control Circuit Low (Bank 1 Sensor 2)
P0038 HO2S Heater Control Circuit High (Bank 1 Sensor 2)
P0039 Turbo/Super Charger Bypass Valve Control Circuit Range/Performance
P0040 O2 Sensor Signals Swapped Bank 1 Sensor 1/ Bank 2 Sensor 1
P0041 O2 Sensor Signals Swapped Bank 1 Sensor 2/ Bank 2 Sensor 2
P0042 HO2S Heater Control Circuit (Bank 1 Sensor 3)
P0043 HO2S Heater Control Circuit Low (Bank 1 Sensor 3)
P0044 HO2S Heater Control Circuit High (Bank 1 Sensor 3)
P0045 Turbo/Super Charger Boost Control Solenoid Circuit/Open
P0046 Turbo/Super Charger Boost Control Solenoid Circuit Range/Performance
P0047 Turbo/Super Charger Boost Control Solenoid Circuit Low
P0048 Turbo/Super Charger Boost Control Solenoid Circuit High
P0049 Turbo/Super Charger Turbine Overspeed
P0050 HO2S Heater Control Circuit (Bank 2 Sensor 1)
P0051 HO2S Heater Control Circuit Low (Bank 2 Sensor 1)
P0052 HO2S Heater Control Circuit High (Bank 2 Sensor 1)
P0053 HO2S Heater Resistance (Bank 1 Sensor 1)
P0054 HO2S Heater Resistance (Bank 1 Sensor 2)
P0055 HO2S Heater Resistance (Bank 1 Sensor 3)
P0056 HO2S Heater Control Circuit (Bank 2 Sensor 2)
P0057 HO2S Heater Control Circuit Low (Bank 2 Sensor 2)
P0058 HO2S Heater Control Circuit High (Bank 2 Sensor 2)
P0059 HO2S Heater Resistance (Bank 2 Sensor 1)
P0060 HO2S Heater Resistance (Bank 2 Sensor 2)
P0061 HO2S Heater Resistance (Bank 2 Sensor 3)
P0062 HO2S Heater Control Circuit (Bank 2 Sensor 3)
P0063 HO2S Heater Control Circuit Low (Bank 2 Sensor 3)
P0064 HO2S Heater Control Circuit High (Bank 2 Sensor 3)
P0065 Air Assisted Injector Control Range/Performance
P0066 Air Assisted Injector Control Circuit or Circuit Low
P0067 Air Assisted Injector Control Circuit High
P0068 MAP/MAF - Throttle Position Correlation
P0069 Manifold Absolute Pressure - Barometric Pressure Correlation
P0070 Ambient Air Temperature Sensor Circuit
P0071 Ambient Air Temperature Sensor Range/Performance
P0072 Ambient Air Temperature Sensor Circuit Low
P0073 Ambient Air Temperature Sensor Circuit High
P0074 Ambient Air Temperature Sensor Circuit Intermittent
P0075 Intake Valve Control Solenoid Circuit (Bank 1)
P0076 Intake Valve Control Solenoid Circuit Low (Bank 1)
P0077 Intake Valve Control Solenoid Circuit High (Bank 1)
P0078 Exhaust Valve Control Solenoid Circuit (Bank 1)
P0079 Exhaust Valve Control Solenoid Circuit Low (Bank 1)
P0080 Exhaust Valve Control Solenoid Circuit High (Bank 1)
P0081 Intake Valve Control Solenoid Circuit (Bank 2)
P0082 Intake Valve Control Solenoid Circuit Low (Bank 2)
P0083 Intake Valve Control Solenoid Circuit High (Bank 2)
P0084 Exhaust Valve Control Solenoid Circuit (Bank 2)
P0085 Exhaust Valve Control Solenoid Circuit Low (Bank 2)
P0086 Exhaust Valve Control Solenoid Circuit High (Bank 2)
P0087 Fuel Rail/System Pressure - Too Low
P0088 Fuel Rail/System Pressure - Too High
P0089 Fuel Pressure Regulator 1 Performance
P0090 Fuel Pressure Regulator 1 Control Circuit
P0091 Fuel Pressure Regulator 1 Control Circuit Low
P0092 Fuel Pressure Regulator 1 Control Circuit High
P0093 Fuel System Leak Detected - Large Leak
P0094 Fuel System Leak Detected - Small Leak
P0095 Intake Air Temperature Sensor 2 Circuit
P0096 Intake Air Temperature Sensor 2 Circuit Range/Performance
P0097 Intake Air Temperature Sensor 2 Circuit Low
P0098 Intake Air Temperature Sensor 2 Circuit High
P0099 Intake Air Temperature Sensor 2 Circuit Intermittent/Erratic

Check the water control valve behind the engine close to the firewall. This valve opens and closes to allow hot coolant to enter the heater core. It is usually connected to the heater controls with a cable. When you adjust the heater control for heat, a cable activated lever on the valve should move and allow coolant to move through the valve. The cable from the heater control can come loose from the lever, or the valve itself can become corroded and hard to move.

THIS LIGHT IS TURNED ON BY ONE OF WELL OVER 200 DIFFERENT PROBLEMS IN THE ELECTRONIC CONTROLS OF THE ENGINE. TRANSMISSION OR EMISSION CONTROL SYSTEM, IN ORDER TO HAVE ANY HOPE OF FINDING THE ROOT CAUSE THE DEALER MUST TEST THE SYSTEM WITH A SPECIAL SCANNER TO SEE WHAT TROUBLE CODES ARE PRESENT, BELOW U WILL FIND A PARTIAL LIST OF THE FAULTS THAT CAN BE PRESENT WHENEVER THE LIGHT IS ON..
P0001 Fuel Volume Regulator Control Circuit/Open
P0002 Fuel Volume Regulator Control Circuit Range/Performance
P0003 Fuel Volume Regulator Control Circuit Low
P0004 Fuel Volume Regulator Control Circuit High
P0005 Fuel Shutoff Valve Control Circuit/Open
P0006 Fuel Shutoff Valve Control Circuit Low
P0007 Fuel Shutoff Valve Control Circuit High
P0008 Engine Position System Performance (Bank 1)
P0009 Engine Position System Performance (Bank 2)
P0010 A Camshaft Position Actuator Circuit (Bank 1)
P0011 A Camshaft Position - Timing Over - Advanced or System Performance (Bank 1)
P0012 A Camshaft Position - Timing Over - Retarded (Bank 1)
P0013 B Camshaft Position - Actuator Circuit (Bank 1)
P0014 B Camshaft Position - Timing Over - Advanced or System Performance (Bank 1)
P0015 B Camshaft Position - Timing Over - Retarded (Bank 1)
P0016 Crankshaft Position - Camshaft Position Correlation (Bank 1 Sensor A)
P0017 Crankshaft Position - Camshaft Position Correlation (Bank 1 Sensor B)
P0018 Crankshaft Position - Camshaft Position Correlation (Bank 2 Sensor A)
P0019 Crankshaft Position - Camshaft Position Correlation (Bank 2 Sensor B)
P0020 A Camshaft Position Actuator Circuit (Bank 2)
P0021 A Camshaft Position - Timing Over - Advanced or System Performance (Bank 2)
P0022 A Camshaft Position - Timing Over-Retarded (Bank 2)
P0023 B Camshaft Position - Actuator Circuit (Bank 2)
P0024 B Camshaft Position - Timing Over - Advanced or System Performance (Bank 2)
P0025 B Camshaft Position - Timing Over - Retarded (Bank 2)
P0026 Intake Valve Control Solenoid Circuit Range/Performance (Bank 1)
P0027 Exhaust Valve Control Solenoid Circuit Range/Performance (Bank 1)
P0028 Intake Valve Control Solenoid Circuit Range/Performance (Bank 2)
P0029 Exhaust Valve Control Solenoid Circuit Range/Performance (Bank 2)
P0030 HO2S Heater Control Circuit (Bank 1 Sensor 1)
P0031 HO2S Heater Control Circuit Low (Bank 1 Sensor 1)
P0032 HO2S Heater Control Circuit High (Bank 1 Sensor 1)
P0033 Turbo Charger Bypass Valve Control Circuit
P0034 Turbo Charger Bypass Valve Control Circuit Low
P0035 Turbo Charger Bypass Valve Control Circuit High
P0036 HO2S Heater Control Circuit (Bank 1 Sensor 2)
P0037 HO2S Heater Control Circuit Low (Bank 1 Sensor 2)
P0038 HO2S Heater Control Circuit High (Bank 1 Sensor 2)
P0039 Turbo/Super Charger Bypass Valve Control Circuit Range/Performance
P0040 O2 Sensor Signals Swapped Bank 1 Sensor 1/ Bank 2 Sensor 1
P0041 O2 Sensor Signals Swapped Bank 1 Sensor 2/ Bank 2 Sensor 2
P0042 HO2S Heater Control Circuit (Bank 1 Sensor 3)
P0043 HO2S Heater Control Circuit Low (Bank 1 Sensor 3)
P0044 HO2S Heater Control Circuit High (Bank 1 Sensor 3)
P0045 Turbo/Super Charger Boost Control Solenoid Circuit/Open
P0046 Turbo/Super Charger Boost Control Solenoid Circuit Range/Performance
P0047 Turbo/Super Charger Boost Control Solenoid Circuit Low
P0048 Turbo/Super Charger Boost Control Solenoid Circuit High
P0049 Turbo/Super Charger Turbine Overspeed
P0050 HO2S Heater Control Circuit (Bank 2 Sensor 1)
P0051 HO2S Heater Control Circuit Low (Bank 2 Sensor 1)
P0052 HO2S Heater Control Circuit High (Bank 2 Sensor 1)
P0053 HO2S Heater Resistance (Bank 1 Sensor 1)
P0054 HO2S Heater Resistance (Bank 1 Sensor 2)
P0055 HO2S Heater Resistance (Bank 1 Sensor 3)
P0056 HO2S Heater Control Circuit (Bank 2 Sensor 2)
P0057 HO2S Heater Control Circuit Low (Bank 2 Sensor 2)
P0058 HO2S Heater Control Circuit High (Bank 2 Sensor 2)
P0059 HO2S Heater Resistance (Bank 2 Sensor 1)
P0060 HO2S Heater Resistance (Bank 2 Sensor 2)
P0061 HO2S Heater Resistance (Bank 2 Sensor 3)
P0062 HO2S Heater Control Circuit (Bank 2 Sensor 3)
P0063 HO2S Heater Control Circuit Low (Bank 2 Sensor 3)
P0064 HO2S Heater Control Circuit High (Bank 2 Sensor 3)
P0065 Air Assisted Injector Control Range/Performance
P0066 Air Assisted Injector Control Circuit or Circuit Low
P0067 Air Assisted Injector Control Circuit High
P0068 MAP/MAF - Throttle Position Correlation
P0069 Manifold Absolute Pressure - Barometric Pressure Correlation
P0070 Ambient Air Temperature Sensor Circuit
P0071 Ambient Air Temperature Sensor Range/Performance
P0072 Ambient Air Temperature Sensor Circuit Low
P0073 Ambient Air Temperature Sensor Circuit High
P0074 Ambient Air Temperature Sensor Circuit Intermittent
P0075 Intake Valve Control Solenoid Circuit (Bank 1)
P0076 Intake Valve Control Solenoid Circuit Low (Bank 1)
P0077 Intake Valve Control Solenoid Circuit High (Bank 1)
P0078 Exhaust Valve Control Solenoid Circuit (Bank 1)
P0079 Exhaust Valve Control Solenoid Circuit Low (Bank 1)
P0080 Exhaust Valve Control Solenoid Circuit High (Bank 1)
P0081 Intake Valve Control Solenoid Circuit (Bank 2)
P0082 Intake Valve Control Solenoid Circuit Low (Bank 2)
P0083 Intake Valve Control Solenoid Circuit High (Bank 2)
P0084 Exhaust Valve Control Solenoid Circuit (Bank 2)
P0085 Exhaust Valve Control Solenoid Circuit Low (Bank 2)
P0086 Exhaust Valve Control Solenoid Circuit High (Bank 2)
P0087 Fuel Rail/System Pressure - Too Low
P0088 Fuel Rail/System Pressure - Too High
P0089 Fuel Pressure Regulator 1 Performance
P0090 Fuel Pressure Regulator 1 Control Circuit
P0091 Fuel Pressure Regulator 1 Control Circuit Low
P0092 Fuel Pressure Regulator 1 Control Circuit High
P0093 Fuel System Leak Detected - Large Leak
P0094 Fuel System Leak Detected - Small Leak
P0095 Intake Air Temperature Sensor 2 Circuit
P0096 Intake Air Temperature Sensor 2 Circuit Range/Performance
P0097 Intake Air Temperature Sensor 2 Circuit Low
P0098 Intake Air Temperature Sensor 2 Circuit High
P0099 Intake Air Temperature Sensor 2 Circuit Intermittent/Erratic

Take it to Autozone or Advanced auto and get an engine diagnostic and ask them to printout the results. Most times it's a sensor.

the temp blend door may not be rotating from the a/c evaporator to the heater core opening.

Could be the motor on the blend door or the temp control knob.

Do you have manual a/c or electronic temp control?

If it's the a/c door electronic actuator motor, it's on top of the plenum. Have to remove the instrument panel for access.

Hope it's the temp knob on the control head.

top one is the circuit you are looking at

Check your coolant level first. Next check your heater control valve. With engine at operating temp and heater on high, do this:

1. Heater hose from water pump should be hot (if not, water pump may be dead or thermostat is stuck closed)
2. Heater hose from thermostat housing should be hot (if not, thermostat may be stuck closed or water pump is dead)
3. Heater hose going to heater core should be hot ( if not, heater control valve is not getting vacuum from heater control unit, or valve is broken)
4. Heater hose returning from heater core should be hot (if not, heater core is blocked, undo both hoses to core and flush with water hose until clear)

Test thermostat: with cold engine cranked, watch water temp gauge. As it gets hotter and hotter, when the thermostat opens, the temp should drop suddenly and then go back up.

Test water pump: with engine at operating temp. Squeeze top radiator hose tight, when you release it, you should feel/hear a surge of water. It is much like when you pinch a water hose closed and release it.

Test vacuum from heater control unit to heater control valve: undue vacuum line from control valve. It should have a vacuum when pressed against you skin in addition to releasing the actuating arm on the control valve.

If there is no vacuum, a quick fix will be to disconnect the plastic actuator from the silver arm on the heater valve. This will let the hot water to always flow to your heater core.