32 (NB6 Emission Vehicles) Linear Exhaust Gas Recirculation (EGR) System

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Description

The PCM controls the amount of EGR flow by sending a PWM ground signal to a linear EGR module (EGR valve signal modifier module assembly). Since the PCM does not have the capability to control the valve directly the linear EGR module reads the PCM, amplifies the signal to operate the valve.

The EGR solenoid also incorporates a position feedback circuit which sends a signal to the PCM indicating the location of the pintle. This sensor provides closed loop control of EGR as well as diagnostics. When the valve is closed the normal pintle position voltage should be between 0.3 and 1.2 volts.

A scan tool can be used to monitor the position feedback voltage. This parameter is located in the General Information table. The following parameters can be found in the Fuel and Emission table.

   * % EGR - Indicates the amount of EGR as calculated by the ECM.
   * Desired Position - Percent EGR pintle opening commanded by the PCM.
   * Actual Position - Percent open of the EGR pintle.

DTC Parameters

There are two different parts to DTC 32 A and B.

  1. Under certain driving conditions the PCM will turn off the signal to the module causing the EGR valve to close. The PCM then monitors the oxygen sensor and how much affect it has on the short term fuel trim. If the fuel trim does not move a calibrated amount and the test fails three times in a row, a DTC 32 will set. This test is performed when:
         o MAP is between 25 and 65 kPa (172 and 448 psi).

Note: At altitude MAP may differ up to 15 kPa (103 psi).

   * VSS is above 32 km/H (20 mph).
   * 20% Desired pintle position.
   * TP sensor is between 5 and 50% and steady.
   * 8 Count integrator change must occur within five seconds.
  2. The PCM constantly monitors the position feedback signal. DTC 32 will set if the voltage is ever below 0.10 volts or if the actual position does not closely match the desired position after 25 seconds (10% or 26 counts).

Test 1 Description

  1. Vehicle speed is required to turn EGR on. When all the conditions are met to command EGR on. it will be indicated by the desired position. This step will verify EGR control as well as the ability of the position sensor to feedback information to the PCM. Be sure DTC 32 is not currently set when running this test. IMPORTANT: This test may result in an ABS code. Percent open values that are displayed for actual and desired position may van slightly.
  2. By grounding circuit 697 the EGR module should command the linear valve all the way open. This will result in a DTC 26 or 27 when performed with engine running.
  3. If the engine starts to run rough or stalls when commanding EGR full on, it indicates the system is functioning properly at this time. If RPM does not change, but the pintle position moved in step 1. it indicates the passages may be plugged. At this point, the valve must be removed and possible restrictions corrected.
  4. This step will determine if the EGR module has the ability to pull to ground circuit 698.

Test 2 Description

  1. If DTC 32 is the only DTC that sets at idle after the diagnostic trouble codes have been cleared, the problem is in the position feedback portion of the system. Since the valve is turned off at idle or with ignition on, the voltage reading should be between 0.3 and 1.2 volts. If viewing desired or actual position in the fuel and emission table 0% should be indicated during this step.
  2. DTC 32 may have set during the above step due to a position feedback sensor being stuck at some voltage level or due to the EGR module commanding the valve partially open. This step will determine if the fault is in the module or the valve. NOTE: This step will result in a DTC 26 due to the voltage being low at pin J2A05 which should be ignored.
  3. If the engine is running rough or will not idle it may be due to EGR being on. which is also indicated by the pintle voltage being above 4 volts.

Test 3 Description

  1. This diagnostic chart assumes that DTC 26 and 32 were related, therefore, it is important that other QDM functions are operating properly before diagnosing potential EGR problem. If there is a QDM problem data in the general information table will indicate if the problem is in QDM-A or QDM-B.
  2. When the engine is at idle EGR is commanded Off. During this condition the linear EGR module should be supplying 12 volts to the PCM pin J2A05. If DTC 26 and 27 are set, the problem is due to a low voltage being detected on circuit 697.
  3. A blown EGR fuse would result in a DTC 26 due to the low voltage on circuit 697.

Diagnostic Aids

When attempting to diagnose an intermittent problem use the Scan tool and review the MALF history supplemental code information. The supplemental data may help indicate when the problem occurred.

If MALF history indicates DTC 26 and 32 were set and no other quad driver related complaints were detected. the DTC 32 was probably set due to a problem in circuit 697. the linear EGR module or possibly the PCM.

When the fuel trim/oxygen sensor portion (part A) of the diagnostics is performed the EGR valve is commanded off and the actual pintle position will go to 0% and desired will read some % value. If this test fails three times and DTC 32 sets the actual position will read 0%. However, the desired position may indicate some other value. This is due to desired position, is always being calculated by the PCM even if the valve is not actually commanded on.

If DTC 32B is detected, check the desired and actual pintle position. If both of these parameters have a percent open value in them, but they do not closely match each other, the sensor may be sticking in a certain position.

  • If DTC 32A continues to set inspect EGR pintle for carbon build-up.
  • Make sure EGR valve gasket and EGR valve are installed correctly or a vacuum leak will occur.