Description
DATA TROUBLE CODE: 71SYSTEM: EGR System Malfunction (Federal)
CIRCUIT DESCRIPTION
The Exhaust Gas Recirculation system is designed to recirculate the exhaust gas, properly controlled according to the driving condition, back into the intake air-fuel mixture. It helps to slow down combustion in the cylinder and thus lowers the combustion temperature which, in turn, reduces the amount of NOx emission. The amount of Exhaust Gas Recirculation is regulated by the Exhaust Gas Recirculation Vacuum Modulator according to the engine load.
If even one of the following conditions is fulfilled, the Vacuum Switching Valve is turned ON by a signal from the Engine Control Module. This results in atmospheric air acting on the Exhaust Gas Recirculation Valve, closing the Exhaust Gas Recirculation Valve and shutting off the exhaust gas (Exhaust Gas Recirculation cut-OFF).
- Engine coolant temperature below 53°C (127°F)
- During decelleration (throttle valve closed)
- Light engine load (amount of intake air very small).
- Engine speed over 4,000 rpm.
- Engine idling.
- Park/Neutral position switch ON.
DIAGNOSTIC TROUBLE CODE DETECTING CONDITION
- Exhaust Gas Recirculation gas temperature is 65°C (149°F) or below for 1 to 4 minutes under the following conditions; (2 trip detection logic)
- Engine coolant temperature is 65°C (149°F) or more.
- Exhaust Gas Recirculation operation possible (A/T in 3rd speed, 5th for M/T, A/C ON, 60 mph, Flat road).
TROUBLE AREA
- Open in Exhaust Gas Recirculation Gas Temperature Sensor circuit.
- Short in Vacuum Switching Valve circuit for Exhaust Gas Recirculation.
- Exhaust Gas Recirculation hose disconnected, valve stuck.
- Clogged Exhaust Gas Recirculation gas passage.
- Engine Control Module.
DIAGNOSTIC TROUBLE CODE DETECTION DRIVING PATTERN
Purpose Of The Driving Pattern
To simulate Diagnostic Trouble Code detecting condition after Diagnostic Trouble Code is recorded. To check that the malfunction is corrected when the repair is completed confirming that Diagnostic Trouble Code is no longer detected.
1. Disconnect the EFI fuse (30 A) for 10 seconds or more with Ignition Switch OFF. Initiate test mode (Connect terminal TE2 and E1 of Data Link Connector 1 or 2 with Ignition Switch OFF).
2. Start the engine and warm up.
3. After the engine is warmed up, let it idle for 3 minutes.
4. With the A/C ON and transmission in 3rd speed drive at 55 - 60 mph for 4 min or less.
NOTE: If the conditions in this test are not strictly followed, detection of the malfunction will not be possible. If a malfunction exists, the malfunction indicator lamp will light up during step 4.
Malfunction Indicator Lamp
Normal Mode On
Test Mode On