Description
DATA TROUBLE CODE: 71SYSTEM: EGR System Malfunction
CIRCUIT DESCRIPTION
The exhaust gas recirculation (EGR) system is designed to recirculate a metered amount of exhaust gas back into the intake air-fuel mixture. The amount of EGR is regulated by the EGR vacuum modulator according to the engine load. Recirculated exhaust gas helps to slow down combustion in the cylinder and thus lowers peak combustion temperatures which, in turn, reduces the amount of NOx emission.
If even ONE (1) of the following conditions is fulfilled, the vacuum switching valve (VSV) is turned ON (open) by a signal from the ECM. This allows the ported vacuum source for the EGR valve to be vented, allowing atmospheric pressure to close the EGR Valve, shutting off the flow of exhaust gas to the intake manifold.
- Engine coolant temperature is 50°C (122 °F) for A/T
- During deceleration (throttle valve closed)
- Light engine load (amount of intake air very small).
- Engine speed over 4,800 rpm.
- Manifold absolute pressure is more than 120kPa (1.2 kg/cm2; 17.4 psi)
DIAGNOSTIC TROUBLE CODE DETECTING CONDITION
EGR gas temperature is 60°C (140°F) for A/T {55°C (131°F) for M/T} or below for 1 to 4 minutes under conditions (a) and (b):
(2 trip detection logic)
(a) Engine coolant temperature is 60°C (140°F) or more.
(b) EGR operation possible (A/T in 3rd gear ()M/T in 5th gear, A/C ON, 60 mph (96 km/h), Flat road).
TROUBLE AREA
- Open in EGR gas temperature sensor circuit.
- Short in VSV for Exhaust Gas Recirculation (EGR) circuit.
- EGR hose disconnected, valve stuck.
- Clogged EGR gas passage.
- ECM
DIAGNOSTIC TROUBLE CODE DETECTION DRIVING PATTERN
Purpose Of The Driving Pattern
- To simulate diagnostic trouble code detecting condition after DTC 71 is recorded.
- To check that the malfunction is corrected when the repair is completed confirming that diagnostic trouble code is no longer detected.