Code 71 (PRIZM - CALIF. Emissions) - Exhaust Gas: Notes

RECIRCULATION (EGR) SYSTEM

Exhaust Gas Recirculation (EGR) temperature sensor is a thermistor in series with a fixed resistor in ECM. ECM applies 5 volts to sensor. ECM monitors voltage across EGR temperature sensor and converts it into a temperature reading. When exhaust gases are cold, EGR temperature sensor resistance is high. When exhaust gases are warm, EGR temperature sensor resistance is low. Therefore, when exhaust gases are cold, ECM receives a high voltage input and when exhaust gases are warm, ECM receives a low voltage input. EGR Solenoid Vacuum (SV) valve is also controlled by ECM. EGR SV valve permits exhaust gas to be recirculated and incorporated into combustion process. ECM by monitoring exhaust gas temperature will determine when to energize EGR SV valve. Code 71 will set if engine coolant temperature is greater than 140°F (60°C) with EGR temperature less than 158°F (70°C) for at least 50 seconds.

1. Checks power feed to sensor.
2. Checks ground circuit to sensor.
3. Checks EGR temperature resistance vs. temperature values.
4. Checks power feed circuit to EGR SV valve.
5. Checks for a faulty EGR SV valve, mechanical checks and a faulty ECM.