DTC 71

Exhaust Gas Recirculation - Part 1 Of 2:

Exhaust Gas Recirculation - Part 2 Of 2:

Exhaust Gas Recirculation:

Circuit Description:
The exhaust gas recirculation (EGR) temperature sensor is a thermistor (a variable resistor that changes along with EGR temperature changes) in series with a fixed resistor within the engine control module (ECM). The ECM applies 5 volts to the sensor. The ECM monitors the voltage across the EGR temperature sensor and converts it into a temperature reading. When the exhaust gases are cold the sensor resistance is high, and when the exhaust gases are warm the sensor resistance is low. Therefore, when the exhaust gases are cold the ECM will receive a high voltage input, and when the exhaust gases are warm the ECM will receive a low voltage input. The ECM also maintains control over a EGR solenoid vacuum (SV) valve. The EGR SV valve permits exhaust gas to be recirculated and incorporated into the combustion process. The ECM will determine the best time to energize the EGR SV valve by monitoring the exhaust gas temperature.

DTC 71 will set if the following condition is met:

^ With ECT above 60° C (140° F) with EGR temperature less than 70° C (158° F) for at least 50 seconds.

Test Description:
Numbers below refer to circled numbers on the diagnostic chart.
1. This checks the power feed to the sensor.

2. This checks the ground circuit to the sensor.

3. This checks the EGR temperature resistance vs. temperature values.

4. This checks the power feed circuit to the EGR SV valve.

5. This checks for a faulty EGR SV valve, mechanical checks and for a faulty ECM.


Diagnostic Aids:
Check EGR vacuum modulator and EGR valve for sticking open or closed.
An intermittent may be caused by a poor connection, rubbed through wire insulation, or a wire broken inside the insulation. Inspect hamess connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals and poor terminal-to-wire connections before component replacement.