DTC P0402 Exhaust Gas Recirculation (EGR) Flow Excessive. Geo Prizm 1997

For 1990-2009 cars

Schematic Reference: Engine Controls Schematics

### Circuit Description

The Exhaust Gas Recirculation (EGR) system recirculates exhaust gas, which is controlled to the proper quantity to suit the driving conditions, into the intake air mixture to slow down combustion, reduce the combustion temperature and reduce NOx emissions. The amount of EGR is regulated by the EGR pressure transducer valve according to the engine load. If one of the following conditions takes place, the EGR vacuum regulator solenoid is turned "OFF" by a signal from the PCM. This results in atmospheric air acting on the EGR valve, closing the EGR valve and shutting off the exhaust gas.

### Conditions for Setting the DTC

• | The intake manifold absolute pressure is greater than the value calculated by the PCM while the EGR system is "ON."

• | Misfiring is detected during idling

• | Engine NOT at operating temperature.

• | During deceleration (throttle valve closed)

• | Light engine load

• | Engine speed over 4,400 RPM.

### Action Taken When the DTC Sets

• | The PCM will illuminate the MIL during the second key cycle in which the DTC sets.

• | The PCM will store the conditions which were present when the DTC set as Freeze Frame Data.

### Conditions for Clearing the MIL/DTC

• | The PCM will turn the MIL "OFF" on the third consecutive trip cycle during which the diagnostic has been run and the fault condition is no longer present.

• | A DTC will clear after 40 consecutive warm-up cycles have occurred without a fault.

• | A DTC can be cleared by using the scan tool "Clear Information" function or by disconnecting the PCM battery feed.

### Diagnostic Aids

• | The EGR valve and EGR pressure transducer should be check for being stuck open.

• | An intermittent malfunction may be cause by a poor connection, rubbed through wire insulation, or a broken wire inside the insulation. Inspect harness connectors for backed out terminals, improper matting, broken locks, terminal-to wire connection before component replacement.

• | If DTC P0401 and DTC P0402 are both set, refer to DTC P0402 first.

• | Check MAP sensor, check for a skewed or stuck MAP sensor value.

• | If The information included in the Freeze Frame data can be useful in determining the vehicle operating conditions when the DTC first set.

### Test Description

The numbers below refer to the step numbers in the Diagnostic Table.

1. The OBD System Check 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. If the vehicle is running rough or stalls with the vacuum hose disconnected from the EGR valve, the malfunction may be cause by the EGR valve being stuck open.

3. This step checks whether DTC P0402 is the result of a hard failure or an intermittent condition.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Was the "Powertrain On Board Diagnostic (OBD) System Check performed? | -- | Go to Step 2 | Go to Powertrain Control Module Connector End Views
2 | Start and run the engine. Does the engine run rough or stall? | -- | Go to Step 4 | Go to Step 3

3

1. Clear the DTC.
2. Using the scan tool, place the vehicle into Check Mode.
3. Operate vehicle within "Freeze Frame" conditions as noted.

Is DTC P0402 set?

--

Go to Step 4

Go to Diagnostic Aids

4

1. Remove EGR valve and visually/physically inspect the valve for the following conditions:

• | Valve pintle for correct seating

• | Valve pintle stuck partly open

• | Carbon deposits or burrs

• | EGR valve gasket torn or missing

• | Vacuum hose routing

2. Repair or replace as necessary.

Was a problem found?

--

Go to Step 16

Go to Step 5

5

1. Turn the ignition switch ON.
2. Disconnect the EGR vacuum regulator solenoid electrical connector.
3. Using a DVM, measure voltage at the EGR vacuum regulator solenoid power feed circuit terminal 2.

Does the DVM read within specified value?

10-12 V

Go to Step 6

Go to Step 10

6

1. Turn the ignition switch ON, engine OFF.
2. Using a test light connected to battery voltage, probe the EGR vacuum regulator control terminal 1.

Does the test light illuminate?

--

Go to Step 11

Go to Step 7

7 | Using a DMM, measure the resistance of the EGR vacuum regulator solenoid. Does the DMM read within the specified value? | 37-44 ohms | Go to Step 8 | Go to Step 14
8 | Using a DMM, check for continuity between the outer casing and each terminal of the EGR vacuum regulator solenoid. Does DMM show continuity on either terminal? | -- | Go to Step 14 | Go to Step 9

9

1. Place your finger over port G (filter side) of the EGR vacuum regulator solenoid.
2. Blow air into port E.

Does the air pass through EGR vacuum regulator vacuum valve and out port F?

--

Go to Step 14

Go to Step 12

10 | Check for an open or short to the EGR vacuum regulator solenoid power feed circuit. Is the action complete? | -- | Go to Step 16 | --

11

1. Check for a short to ground to the EGR vacuum regulator solenoid control circuit.
2. Repair as necessary.

Was a repair necessary?

--

Go to Step 16

Go to Step 15

12

1. Check ported vacuum hoses connected to the EGR pressure transducer for correct routing.
2. Repair as necessary.

Was a repair necessary?

--

Go to Step 16

Go to Step 13

13 | Replace the EGR Pressure Transducer. Is the action complete? | -- | Go to Step 16 | --
14 | Replace the EGR vacuum regulator solenoid. Is the action complete? | -- | Go to Step 16 | --
15 | Replace the PCM. Is the action complete? | -- | Go to Step 16 | --
16 | After repairs, use the scan tool clear information function and road test vehicle within "Freeze Frame" conditions that set the DTC. Check for DTC(s). Review scan tool data and if no DTC(s) are stored repair is complete. Are any DTC(s) displayed on scan tool? | -- | Go to the applicable DTC table | System OK