DTC 51

***THIS ARTICLE INCLUDES UPDATES MADE BY TECHNICAL SERVICE BULLETIN 61-65-21, DATED APRIL, 1996***

Diagnostic Chart:

Electrical Schematic:

CIRCUIT DESCRIPTION
The Exhaust Gas Recirculation Temperature (EGRT) sensor is mounted on top of the EGR valve. The sensor has a variable resistor that changes along with the temperature of the exhaust gases. The Engine Control Module (ECM) applies 5 volts to the sensor and reads the voltage across the sensor. As the exhaust gas temperature increases, the sensor's resistance decreases, providing the ECM with a low voltage input. When the exhaust gas temperature decreases, the sensor's resistance increases, providing the ECM with a high voltage input. The ECM calculates the temperature of the exhaust gases by voltage inputs it receives.

Diagnostic Trouble Code (DTC) 51 will set if one of the following conditions are met:
- Condition 1: Exhaust gas temperature lower than 80°C (176°F) is sensed for 5 seconds when all of the following conditions are met simultaneously for 30 seconds:
(1) Charging efficiency between 30 - 58%.
(2) Exhaust Gas Recirculation Solenoid Vacuum (EGR SV) valve "OFF."
(3) Engine coolant temperature more than 75°C (167°F).
(4) Mass air flow rate between 10.2-28.2 g/sec.

- Condition 2: When the following two conditions are met:
(1) Engine coolant temperature less than 40°C (104°F).
(2) Exhaust gas temperature higher than 220°C (428°F).

- Condition 3: Exhaust gas temperature lower than -10°C (14°F) is sensed for 3 seconds when the engine coolant temperature has been higher than 70°C (150°F) for more than 80 seconds.

CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. Checks for proper EGR valve operation.
2. Checks for 5 volt reference to the EGRT sensor.
3. Checks for a short to voltage in RED/GRN wire.
4. Checks for an open GRY/YEL wire, a faulty ECM or a faulty EGRT sensor.

DIAGNOSTIC AIDS
Intermittent Malfunctions
An intermittent malfunction may be caused by a poor connection, rubbed through wire insulation, or a wire broken inside the insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals and poor terminal-to-wire connections before component replacement.