Toyota Corolla 1988-1997 Repair Guide

Cold Mixture Heater


This system is only used on the 4A-F engines.


The Cold-Mixture Heater (CMH) system reduces cold engine emissions and improves driveability during engine warm-up. The intake manifold is heated during cold engine warm-up to accelerate vaporization of the fuel.

If the engine is running and the coolant temperature is below a predetermined limit, the computer energizes the cold mixture heater relay. This in turn allows battery voltage to be applied to the cold mixture heater. The CMH is a Multi-element heater ring that is mounted between the carburetor base and the intake manifold. Once the coolant temperature exceeds a certain limit, the CMH relay is de-energized and the heater elements turn off.


Mixture Heater Element
  1. Unplug the wiring connector.
  3. Using an ohmmeter, check the resistance between the heater terminals. The resistance should be 0.5-2.2 ohms. Readings outside this range require replacement of the heater element.
  5. Replug the wiring connector.

Mixture Heater Relay

This relay is located on the left fender apron.

  1. Check that there is continuity between the No. 1 and 2 terminals. Check that there is NO continuity between the No. 3 and 4 terminals.
  3. Apply battery voltage to terminal No. 1 and 2. Use the ohmmeter to check for continuity between terminals 3 and 4.