Nissan 240SX/Altima 1993-1998 Repair Guide

Exhaust Gas Recirculation (EGR) System

Print

OPERATION



The Exhaust Gas Recirculation (EGR) system cuts and controls vacuum applied to the EGR valve to suit engine operating conditions. This "cut and control" operation is accomplished through the Electronic Control Module (ECM), in conjunction with an EGR and canister control solenoid valve. When the ECM detects any of the following conditions, current flows through the solenoid valve:



Low engine coolant temperature
 
Engine starting
 
High speed engine operation
 
Engine idling
 
Excessively high engine coolant temperature
 
Mass air flow sensor malfunction
 

Such current flow through the solenoid valve causes port vacuum to be discharged into the atmosphere. The EGR valve and canister remain closed.

The EGR valve controls the amount of exhaust gas routed to the intake manifold. Vacuum is applied to the EGR valve in response to throttle valve opening. The vacuum controls the movement of a taper valve connected to the vacuum diaphragm of the EGR valve.

The EGR and canister control solenoid valve responds to signals from the ECM. When the ECM sends an ON (ground) signal, the coil in the solenoid valve is energized. A plunger will then move to cut the vacuum signal (from the throttle body to the EGR valve and canister purge valve). When the ECM sends an OFF signal, the vacuum signal passes through the solenoid valve. The signal then reaches the EGR valve and canister.

The EGR Backpressure Transducer (EGRC-BPT) valve monitors exhaust pressure to activate the diaphragm, controlling throttle body vacuum applied to the EGR valve. In this way, the recirculated exhaust gas is controlled in response to positioning of the EGR valve or to engine operation.

A negative temperature coefficient EGR temperature sensor is used to control EGR operation timing during warm-up and under conditions when the engine temperature is out of normal range.

SYSTEM TESTING



  1. Start the engine and allow it to reach operating temperature.
  2.  
  3. Check for EGR valve movement while racing the engine from 200-4000 rpm under no load.
  4.  
  5. The EGR valve diaphragm should lift up and down without restriction.
  6.  
  7. If the EGR valve does not respond as specified, perform component testing.
  8.  

COMPONENT TESTING



See Figure 1



Click image to see an enlarged view

Fig. Fig. 1: The EGR valve (1), EGR backpressure transducer (2) and EGR control solenoid valve (3) are all located on the intake manifold, near the firewall

EGR Valve

See Figure 2



Click image to see an enlarged view

Fig. Fig. 2: The EGR function test is performed by using a vacuum pump. Watch for diaphragm movement while applying vacuum

  1. Label and disconnect the EGR valve vacuum hose.
  2.  
  3. Using a hand-held vacuum pump, slowly apply 5-10 in. Hg (17-34 kPa) of vacuum to the EGR valve nipple.
  4.  
  5. The EGR valve diaphragm should lift up. Release the vacuum and the EGR valve diaphragm should lower without restriction.
  6.  
  7. If the EGR valve does not respond as specified, remove the valve and check for obstructions. If no obstructions are found, the EGR valve may be faulty.
  8.  

EGR Backpressure Transducer (EGRC-BPT) Valve
  1. Label and disconnect the transducer valve-s vacuum lines.
  2.  
  3. Plug one of the ports on top of the valve.
  4.  
  5. Blow into the bottom port gently while applying vacuum to the second port on top of the valve. Vacuum should hold steady and not leak.
  6.  
  7. Stop blowing into the bottom port and vacuum should leak out.
  8.  
  9. If the valve does not respond as specified, it may be faulty.
  10.  

EGR Control Solenoid Valve

See Figure 3



Click image to see an enlarged view

Fig. Fig. 3: EGR control solenoid valve port identification

  1. Label and disconnect the solenoid valve electrical harness and vacuum lines.
  2.  
  3. Air should pass through Ports A and B freely.
  4.  
  5. Apply battery voltage and ground to the solenoid terminals.
  6.  
  7. Air should not pass through Ports A and B freely.
  8.  
  9. Air should now pass through Ports A and C freely.
  10.  
  11. If the valve does not respond as specified, it may be faulty.
  12.  
  13. If the valve responds as specified, check and repair the power and ground circuits.
  14.  

EGR Temperature Sensor
  1. Disconnect the temperature sensor electrical harness and measure the resistance between the sensor terminals.
  2.  
  3. Resistance should be high when the sensor is cold and low when the sensor is hot.
  4.  
  5. Compare the cold and hot EGR temperature sensor resistance measurements with the accompanying chart.
  6.  
  7. If resistance is not within specifications or does not respond smoothly as temperature rises and falls, the sensor may be faulty.
  8.  
  9. If the sensor responds as specified, check and repair the power and ground circuits.
  10.  

See Figure 4

Click image to see an enlarged view

Fig. Fig. 4: EGR Temperature Sensor

REMOVAL & INSTALLATION



See Figure 5



Click image to see an enlarged view

Fig. Fig. 5: The EGR backpressure transducer and EGR control solenoid valve fasteners (arrows) are plainly visible

EGR Valve

See Figures 6 and 7



Click image to see an enlarged view

Fig. Fig. 6: The EGR valve port (arrow) allows exhaust gas to flow into the intake manifold



Click image to see an enlarged view

Fig. Fig. 7: The EGR valve gasket is made of a special, high temperature material. Always replace it with a gasket made especially for EGR valves

The EGR valve is located on the intake manifold.

  1. Label and disconnect the EGR vacuum lines.
  2.  
  3. Loosen the EGR valve attaching nuts, then separate the valve from the intake manifold.
  4.  
  5. Remove and discard the EGR valve gasket.
  6.  

To install:
  1. Throughly clean the gasket mating surfaces on the valve and the intake manifold.
  2.  
  3. Install the EGR valve, along with a new gasket, and tighten the mounting nuts to 12-14 ft. lbs. (16-1 Nm).
  4.  
  5. Connect the EGR vacuum lines.
  6.  

EGR Backpressure Transducer (EGRC-BPT) Valve

The EGR backpressure transducer valve is located on the intake manifold.

  1. Label and disconnect the valve-s vacuum lines.
  2.  
  3. Loosen the valve attaching bolts, then remove the valve from the mounting bracket.
  4.  

To install:
  1. Position the valve and tighten the mounting bolts to 12-14 ft. lbs. (16-1 Nm).
  2.  
  3. Connect the valve-s vacuum lines.
  4.  

EGR Control Solenoid Valve

See Figure 8



Click image to see an enlarged view

Fig. Fig. 8: Label and disconnect the EGR control solenoid valve vacuum hoses

The EGR and canister control solenoid valve is located on the intake manifold.

  1. Label and disconnect the solenoid valve vacuum lines.
  2.  
  3. Loosen the solenoid valve attaching nut, then separate the valve from the intake manifold.
  4.  

To install:
  1. Install the solenoid valve and tighten the mounting nut to 12-14 ft. lbs. (16-1 Nm).
  2.  
  3. Connect the solenoid valve vacuum lines.
  4.  

EGR Temperature Sensor

See Figure 9



Click image to see an enlarged view

Fig. Fig. 9: The EGR temperature sensor (arrow) is located in the intake manifold between cylinders 3 and 4

The EGR temperature sensor is located on the engine block, viewable through the intake manifold runners.

  1. Partially drain the engine cooling system until the coolant level is below the EGR temperature sensor mounting hole.
  2.  
  3. Disconnect the EGR temperature sensor electrical harness.
  4.  
  5. Remove the sensor from the intake manifold.
  6.  

To install:
  1. Coat the sensor threads with Teflon sealant.
  2.  
  3. Thread the sensor into the intake manifold and tighten to 11-18 ft. lbs. (15-7 Nm).
  4.  
  5. Connect the negative battery cable.
  6.  
  7. Refill the engine cooling system.
  8.  
  9. Start the engine and check for coolant leaks. Top off the cooling system.
  10.  

 
label.common.footer.alt.autozoneLogo