Circuit Description
An Exhaust Gas Recirculation (EGR) system is used to lower Oxides of Nitrogen (NOx) emission levels caused by high combustion temperatures. It accomplishes this by feeding small amounts of exhaust gases back into the combustion chamber. When the air/fuel mixture is diluted with the exhaust gases, combustion temperatures are reduced.
A linear EGR valve is used on this system. The linear EGR valve is designed to accurately supply exhaust gases to the engine without the use of intake manifold vacuum. The valve controls exhaust flow going into the intake manifold from the exhaust manifold through an orifice with a PCM controlled pintle. The PCM controls the pintle position using inputs from the Throttle Position (TP) and Manifold Absolute Pressure (MAP) sensors. The PCM then commands the EGR valve to operate when necessary by controlling an ignition signal through the PCM. This can be monitored on a scan tool as the Desired EGR Position.
The PCM monitors the results of its command through a feedback signal. By sending a 5 volt reference and a ground to the EGR valve, a voltage signal representing the EGR valve pintle position is sent to the PCM. This feedback signal can also be monitored on a scan tool and is the actual position of the EGR pintle. The Actual EGR Position should always be near the commanded or Desired EGR Position. The PCM monitors the EGR valve pintle position input to ensure that the valve responds properly to commands from the PCM and to detect a fault if the pintle position sensor circuit is open or shorted. If the PCM detects an excessively low EGR Feedback signal voltage.
Conditions for Running the DTC
| • | No TP, MAF, HO2S, IAT, or ECT DTCs are set. |
| • | Engine run time met. The time ranges from 45 seconds to 8.5 minutes depending upon engine coolant temperature at startup. |
| • | TP angle is greater than 2 percent. |
| • | System voltage is greater than 10 volts. |
Conditions for Setting the DTC
| • | EGR Feedback is less than 0.14 volt at any time. |
| • | The condition is present for longer than 20 seconds. |
Action Taken When the DTC Sets
| • | The PCM will illuminate the MIL during the second consecutive trip in which the diagnostic test has been run and failed. |
| • | The PCM will disable EGR for the rest of the ignition cycle. |
| • | The PCM will store conditions which were present when the DTC set as Freeze Frame and Fail Records data. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn the MIL OFF during the third consecutive trip in which the diagnostic has been run and passed. |
| • | The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction. |
| • | The DTC can be cleared by using the scan tool Clear Info function or by disconnecting the PCM battery feed. |
Diagnostic Aids
| • | Poor connection at PCM or EGR Valve. |
| Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection. |
| • | Damaged harness. |
| Inspect the wiring harness for damage. If the harness appears to be OK, connect J 39200 DMM and check circuit continuity while moving connectors and wiring harnesses related to the EGR valve. A change in the DMM display will indicate the location of the malfunction. |
Test Description
Numbers below refer to the step numbers on the Diagnostic Table:
-
Verifies that the malfunction is present.
-
If DTC P0405 will only set under certain conditions, the malfunction may be intermittent; refer to Diagnostic Aids. If an intermittent wiring problem is not present, check for a poor connection at the PCM or the EGR valve. Refer to Wiring Repairs in Wiring Systems.
-
This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed.
Step | Action | Value(s) | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||||||||
Does Desired EGR Position remain close to Actual EGR Position at all commanded positions? | -- | |||||||||
Does the scan tool indicate DTC P0405 failed this ign? | -- | Go to Diagnostic Aids | ||||||||
4 |
Is the voltage at the specified value? | 5 V | ||||||||
5 | Probe the EGR valve pintle position circuit at the EGR valve harness connector with a test light connected to B+. Is the test light ON? | -- | ||||||||
6 |
Is Actual EGR Position at the specified value? | 100% | ||||||||
7 |
Was a problem found? | -- | ||||||||
8 |
Is the test light ON? | -- | ||||||||
9 | Probe the 5 volt reference circuit with a test light to B+. Is the test light ON? | -- | ||||||||
10 |
Is the test light ON? | -- | ||||||||
11 |
Was a problem found? | -- | ||||||||
12 | Locate and correct the short to ground in the EGR valve pintle position circuit. Refer to Wiring Repairs in Wiring Systems. Is action complete? | -- | -- | |||||||
13 |
Was a problem found? | -- | ||||||||
14 | Replace the EGR valve. Refer to Exhaust Gas Recirculation Valve Replacement . Notice: If the EGR valve shows signs of excessive heat, inspect the exhaust
system for blockage--possibly a plugged converter--using the procedure
found on the Restricted Exhaust System Check. If the exhaust system is restricted,
repair the cause. Inspect for an open injector caused by one or more of the
following conditions:
Is action complete? | -- | -- | |||||||
15 |
Was a problem found? | -- | ||||||||
16 | Locate and repair short to ground in the 5 volt reference A circuit. Refer to Wiring Repairs in Wiring Systems. Is action complete? | -- | -- | |||||||
17 |
Was a problem found? | -- | ||||||||
|
Important:: The replacement PCM must be programmed. Refer to Powertrain Control Module Replacement . Replace the PCM. Is action complete? | -- | -- | ||||||||
19 |
Does the scan tool indicate DTC P0405 failed this ignition? | -- | System OK |
