Toyota Tercel 1984-1994 Repair Guide

Cold Mixture Heater



Used on 3A-C and 3E 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

See Figure 1

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

Click image to see an enlarged view

Fig. Fig. 1: Checking the resistance of the mixture heater element

Mixture Heater Relay

See Figures 2 and 3

  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.

Click image to see an enlarged view

Fig. Fig. 2: Inspecting relay continuity

Click image to see an enlarged view

Fig. Fig. 3: Inspecting relay operation