Nissan Sentra/Pulsar/NX 1982-1996 Repair Guide

Catalyst Warm-up System



See Figures 1, 2 and 3

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Fig. Fig. 1: Catalyst Warm-up System components-E15 and E16 engines with early style system

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Fig. Fig. 2: Catalyst Warm-up System components-E16 and E16S engines with late style MPG system

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Fig. Fig. 3: Catalyst Warm-up System operation

This system was used on 1982-85 vehicles with carburetors. The MPG models are controlled by the ECU.

The catalyst warm-up system increases engine speed during warm-up periods to raise the temperature of the catalyst, thereby decreasing exhaust emissions.

The system consists of a vacuum switching valve, temperature sensor, neutral switch and vacuum delay valve. This system uses the throttle opener servo diaphragm as described earlier in this section.


  1. Start the engine.

The engine must be between 59-104°F (15-40°C) to begin testing. Accurate test results will not be obtained if engine temperatures are not within specifications.

  1. Shift gears to make sure that engine speed increases when gear is in neutral.
  3. Warm the engine above 104°F (40°C) and make sure the engine rpm decreases and does not change when the gear is shifted to neutral. If the engine speed does not vary at all, disconnect the vacuum switching valve.
  5. With the engine running, apply 12 volts to the valve and make sure the engine speed increases and ignition timing retards. If no change occurs, test the vacuum switch, opener servo, distributor and vacuum hoses.