Schematic Reference: Refer to 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 condition 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
| • | Engine at normal operating temperature, the intake manifold absolute pressure is greater than the value calculated by the PCM while the EGR system is ON. |
| • | 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 checked for the following conditions. |
| • | Stuck closed |
| • | Plugged passage |
| • | 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 for a skewed or stuck MAP sensor value |
| • | 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.
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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.
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This step checks whether DTC P0401 is the result of a hard failure or an intermittent condition.
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It may be necessary to perform this operation a few times to see vacuum. If the vacuum gauge fails to read vacuum, then the fault can be isolated to either the EGR valve or a plugged manifold passage. Vacuum may show very quickly on the gauge, this would be considered normal operation.
Step | Action | Value(s) | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Was the "Powertrain On Board Diagnostic (OBD) System Check performed? | -- | |||||||||||
Is DTC P0401 set? | -- | Go to Diagnostic Aids | ||||||||||
Does vacuum gauge read vacuum? | 185-275 ohms at 50°C (122°F) or 240-325 ohms at 100°C (212°F) | |||||||||||
4 |
Does engine run rough or stall? | -- | ||||||||||
5 |
Was a problem found? | -- | ||||||||||
6 |
Does the DMM read within specified range? | 10-12 V | ||||||||||
7 | Using a DMM, measure the resistance of the EGR vacuum regulator solenoid. Does the DMM read within the specified value? | 37-44 ohms | ||||||||||
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? | -- | ||||||||||
9 | Blow air into port "E" of the EGR vacuum regulator solenoid. Does air pass through EGR vacuum regulator solenoid, and out of port "G" (filter side)? | -- | ||||||||||
10 |
Does air pass through EGR vacuum regulator solenoid port "F"? | -- | ||||||||||
11 |
Was a repair necessary? | -- | ||||||||||
12 | Check for an open or short to the EGR vacuum regulator solenoid power feed circuit. Is action complete? | -- | -- | |||||||||
13 |
Is there a strong resistance to air flow? | -- | ||||||||||
14 |
Was a repair necessary? | -- | ||||||||||
15 |
Was a repair necessary? | -- | ||||||||||
16 | Replace the EGR Pressure Transducer. Is the action complete? | -- | -- | |||||||||
17 | Replace the EGR vacuum regulator solenoid. Refer to Exhaust Gas Recirculation Solenoid Vacuum Valve Replacement. Is the action complete? | -- | -- | |||||||||
18 | Replace the EGR valve. Refer to Exhaust Gas Recirculation Valve Replacement. Is the action complete? | -- | -- | |||||||||
19 | Replace the PCM. Refer to Powertrain Control Module Replacement. Is the action complete? | -- | -- | |||||||||
20 | 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 |
