P0402

CIRCUIT DESCRIPTION
The DTC P0402 Exhaust Gas Recirculation (EGR) Flow Excessive diagnostic monitors the operation of the EGR valve. The EGR system controls the formation of oxides of nitrogen (NOx) emissions by recirculating the exhaust gases into the combustion chamber. The powertrain control module (PCM) uses the expected changes in the manifold absolute pressure (MAP) sensor readings in order to evaluate the performance of the EGR system. The PCM sends a signal to the EGR valve while monitoring the MAP sensor signal. The PCM suspects that the EGR valve flow is incorrect when the monitored MAP sensor pressure change is too small.

CONDITIONS FOR RUNNING THE DTC
- DTC P0107 and DTC P0108 are not set.
- The barometric pressure (BARO) is more than or equal to 75 kPa.
- The engine coolant temperature (ECT) is between 70-110°C (158-230°F).
- The intake air temperature (IAT) is between -14 to +70°C (7-158°F).
- The vehicle speed is between 50-65 km/h (30-40 mph).
- The engine speed is between 2,000-3,000 RPM for 3 minutes.
- The throttle valve opening remains constant.

CONDITIONS FOR SETTING THE DTC
The difference in intake manifold pressure between when the EGR valve is OPEN, and when the EGR valve is CLOSED, is more than a specified value.

ACTION TAKEN WHEN THE DTC SETS
- The PCM illuminates the malfunction indicator lamp (MIL) after 2 consecutive ignition cycles in which the diagnostic runs with the fault active.
- The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame buffer.

CONDITIONS FOR CLEARING THE MIL/DTC
- The MIL turns OFF after 3 consecutively passing trips without a fault present.
- A history DTC clears after 40 consecutive warm-up cycles without a fault.
- Perform the scan tool Clear DTC Information function in order to clear the DTC.

DIAGNOSTIC AIDS
Check for any of the following conditions:
- An EGR valve that is stuck open, or binding.
- The incorrect PCM can cause DTC P0402 to set. Check that the correct PCM software calibrations are installed in the vehicle as required for proper emission certification.
- Inspect for the correct wiring of the EGR valve coil control circuits. Crossed or incorrectly located wiring can cause faulty EGR valve operation.
- The DTC P0402 diagnostic test is more likely to run in city driving. Avoid long road tests at highway speeds when attempting to validate a DTC P0402.

A DTC P0402 may set when the expected change in MAP is more than the expected value during the operation of the EGR valve. Investigate any condition that can affect the accuracy of the MAP sensor readings:
- Incorrect ignition timing
- A restricted exhaust system
- A faulty MAP sensor

If a DTC P0402 is intermittent, driving the vehicle under the conditions outlined in the Inspection/Maintenance (I/M) section can verify whether the fault is present. Refer to Inspection/Maintenance (I/M) Exhaust Gas Recirculation (EGR) System Set Procedure. I/M EGR System Set Procedure

If a DTC P0402 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining the vehicle operating conditions when the DTC was first set.

An intermittent malfunction may be caused by a fault in the EGR valve or MAP sensor electrical circuits. Inspect the wiring harness and components for an intermittent condition. Refer to Intermittent Conditions. Intermittent Conditions




Use the table in order to locate the correct terminals to test during diagnosis. The table layout corresponds to the pin location of the EGR valve electrical terminals.

An EGR valve that exhibits excessive flow may have a faulty coil winding. Use a DMM to measure the following EGR valve coil windings for the correct resistance value of 20-24 ohms at 20°C (68°F). Refer to the EGR Valve Terminal Identification table.
- Between pin 1 and pin 2
- Between pin 2 and pin 3
- Between pin 5 and pin 6
- Between pin 4 and pin 5

TEST DESCRIPTION

Steps 1-2:

Steps 3-4:

Steps 5-6:

Steps 7-10:

Steps 11-14:

Steps 15-16:

The number below refer to the step number in the diagnostic table.
1. The Diagnostic System Check-Computers and Control Systems prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
2. This step checks for an EGR valve that is leaking, stuck open, or turned on at idle. Normal engine operating temperature is specified as 80°C (176°F) or above.
3. This step checks the operation of the EGR valve. The duty cycle output control of the EGR is disabled by the PCM when any DTCs are stored and when the engine temperature is less than 80°C (176°F).
6. This step checks for proper manifold absolute pressure (MAP) sensor operation. The diagnostic for a DTC P0402 depends on MAP sensor output in order to monitor EGR valve performance.
7. Fault not present indicates the condition that caused DTC P0402 to set is intermittent and not currently present. If no other DTCs are stored, refer to Diagnostic Aids for additional information on diagnosing an intermittent DTC P0402.
8. This step determines whether an electrical fault is the cause of the EGR valve staying open. An EGR valve control circuit that becomes shorted or open when the EGR valve is open, can cause the valve to remain open all the time.
10. This step checks for an EGR valve control circuit that is shorted to ground. If the circuit wiring is OK, a faulty PCM with an internally shorted circuit can cause the EGR valve to be open.
15. Clearing the DTCs by removing the DOME fuse also clears the PCM long term memory. Using the scan tool to clear DTCs leaves the long term memory active. DTC emitting diagnostics may not run to completion as expected unless the long term memory is cleared. Removal of the DOME fuse also clears the time display of the radio. The DTC P0402 diagnostic can be monitored on the scan tool under the Not Ran Since Code Cleared selection in the DTC Information menu. If a DTC P0402 appears in the Not Ran Since Code Cleared list, the DTC P0402 diagnostic has not yet run. When the DTC P0402 does not appear in the Not Ran Since Code Cleared list, the DTC P0402 diagnostic has run. If the MIL is NOT illuminated, and there is no Pending DTC Status in DTC Information, the DTC P0402 diagnostic has passed. The DTCs MUST be cleared in order to view the Current Status of the Not Ran Since Code Cleared list. DO NOT forget that the Not Ran Since Code Cleared list only indicates that the test has run, not whether the test passed or failed. The DTC Information screen must be checked for Current or Pending status, in order to determine the outcome of the diagnostic test involved.