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Chad
Chad, Lead Master Tech
Category: Chrysler
Satisfied Customers: 1114
Experience:  Electrical master,Diesel Specialist,Lead tech/ shop foreman
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Chrysler Sebring: My check engine light is on for my 2005 Chrysler

Customer Question

My check engine light is on for my 2005 Chrysler Sebring Sedan (2.4 Liter). The code is P0491. What should be checked to fix this problem?
Submitted: 4 years ago.
Category: Chrysler
Expert:  Chad replied 4 years ago.
P0491-AIR INJECTION SYSTEM PERFORMANCE

You will need to replace the Air Injection Pump
Expert:  Chad replied 4 years ago.
  1. Disconnect negative battery cable.
  2. Remove air inlet tube for the air cleaner box.
  3. Disconnect quick connect hose from the top of the air pump.
  4. Raise vehicle and support.
  5. Remove 3 mounting nuts .
  6. Unlock electrical connector.
  7. Unclip electrical connector from mounting bracket.
  8. Press tab and disconnect electrical connector.
  9. Disconnect quick connect hose from inlet of the air pump.
  10. Remove air pump from vehicle .

This is looking up from under the car, next to the lower radiator support.

graphic

Expert:  Chad replied 4 years ago.
Do you have any other questions?
Customer: replied 4 years ago.
Is replacing the only air injection pump, the only possible problem? What else should be checked before replacing? Can you send me a list of other possible checks or problems that P0491 would be the code? Thank you!
Expert:  Chad replied 4 years ago.
You will need the factory DBR3 scan tool.
But everytime I have seen the code P0491 it has been the air pump causing it. And after 1.5 hours of diagnostics I had to replace it.
But I can give you the diag procedure if you would like.

NOTE: Before performing the following test, always check the Air Pump
Assembly in-line connectors. Ensure that there is no terminal damage,
corrosion or backed out terminals. Verify that there is good wire to terminal
connection in the connector
Expert:  Chad replied 4 years ago.
Other possible causes....
VISUAL AND PHYSICAL INSPECTION OF THE AIR INJECTION SYSTEM
ASD RELAY OUTPUT CIRCUIT
MAF SENSOR INTERNAL FAILURE
MAF SIGNAL CIRCUIT SHORTED TO ASD RELAY OUTPUT CIRCUIT
MAF SIGNAL CIRCUIT SHORTED TO BATTERY VOLTAGE
MAF SIGNAL CIRCUIT OPEN
MAF SIGNAL CIRCUIT SHORTED TO GROUND
MAF SIGNAL CIRCUIT SHORTED TO (K4) SENSOR GROUND CIRCUIT
SENSOR GROUND CIRCUIT OPEN
PCM
Chad and 2 other Chrysler Specialists are ready to help you
Expert:  Chad replied 4 years ago.
NOTE: Before performing the following test, always check the Air Pump
Assembly in-line connectors. Ensure that there is no terminal damage,
corrosion or backed out terminals. Verify that there is good wire to terminal
connection in the connector.
Ignition on, engine not running.
With the DRBIIIt, read DTCs and record the related Freeze Frame data.
Is the Good Trip displayed and equal to zero?
Yes ! Go To 2
No ! Refer to the INTERMITTENT CONDITION symptom in the
Driveability category.
Perform POWERTRAIN VERIFICATION TEST VER - 5.
2.Visually and physically inspect the following components for any condition that
would cause a air flow condition.
Inlet Filter- blockage, damage, and obstructions
Inlet Hose - blockage, damage, holes, incorrect installation, and hose integrity (i.e.,
collapsing when the pump is operating).
Air Injection Pump - ensure that there are no cracks or damage to the housing.
Air Injection Pump (Nylon) Tube - blockage, damage, incorrect routing, holes/cracks
and kinks.
Exhaust one-way check valve - blockage, plugged or damage.
Were any of the above conditions found?
Yes ! Repair or replace as necessary.
Perform POWERTRAIN VERIFICATION TEST VER - 5.
No ! Go To 3
3.Turn the ignition off.
Disconnect the MAF Sensor harness connector.
Ignition on, engine not running.
Using the DRBIIIt, actuate the ASD Relay.
With a 12-volt test light connected to ground, probe the ASD Relay Output circuit in
the MAF harness connector.
Does the test light illuminate brightly?
Yes ! Go To 4
No ! Repair the ASD Relay Output circuit
Perform POWERTRAIN VERIFICATION TEST VER - 5.
4.NOTE: Monitor the MAF Sensor voltage on the DRBIIIt while performing
this test. The voltage should start at 5.0 volts and go to 0 volts with the
jumper wire in is place.
Turn the ignition off.
Disconnect the MAF Sensor harness connector.
Turn the ignition on.
Connect a jumper wire between the MAF Sensor Signal circuit and the Sensor
ground circuit.
With the DRBIIIt, monitor the MAF Sensor voltage.
Does the voltage go from 5.0 volts to 0 volts?
Yes ! Replace the MAF Sensor.
Perform POWERTRAIN VERIFICATION TEST VER - 5.
No ! Go To 5
5.Turn the ignition off.
Disconnect the MAF Sensor harness connector.
Disconnect the PCM harness connector.
Measure the resistance between the MAF Signal circuit and the ASD Relay Output
circuit in the MAF Sensor harness connector.
Is the resistance below 100 ohms?
Yes ! Repair the MAF Signal circuit for a short to the ASD Relay
Output circuit.
Perform POWERTRAIN VERIFICATION TEST VER - 5.
No ! Go To 6
6.Turn the ignition off.
Disconnect the MAF Sensor harness connector.
Disconnect the PCM harness connector.
Ignition on, engine not running.
Measure the voltage of the MAF Signal circuit in the MAP Sensor harness connector.
Is any voltage present?
Yes ! Repair the short to battery voltage in the MAF Signal circuit.
Perform POWERTRAIN VERIFICATION TEST VER - 5.
No ! Go To 7
7.Turn the ignition off.
Disconnect the MAF Sensor harness connector.
Disconnect the PCM harness connector.
CAUTION: DO NOT PROBE THE PCM HARNESS CONNECTORS. PROBING
THE PCM HARNESS CONNECTORS WILL DAMAGE THE PCM TERMINALS
RESULTING IN POOR TERMINAL TO PIN CONNECTION. INSTALL
MILLER SPECIAL TOOL #8815 TO PERFORM DIAGNOSIS.
Measure the resistance of the MAF Signal circuit from the MAF Sensor harness
connector to the appropriate terminal of special tool #8815.
Is the resistance below 5.0 ohms?
Yes ! Go To 8
No ! Repair the open in the MAF Signal circuit.
Perform POWERTRAIN VERIFICATION TEST VER - 5.
8.Turn the ignition off.
Disconnect the MAF Sensor harness connector.
Disconnect the PCM harness connector.
Measure the resistance between ground and the MAF Signal circuit at the MAF
Sensor harness connector.
Is the resistance below 100 ohms?
Yes ! Repair the short to ground in the MAF Signal circuit.
Perform POWERTRAIN VERIFICATION TEST VER - 5.
No ! Go To 9
9.Turn the ignition off.
Disconnect the MAF Sensor harness connector.
Disconnect the PCM harness connector.
Measure the resistance between the MAF Signal circuit and the Sensor ground
circuit in the MAF Sensor harness connector.
Is the resistance below 100 ohms?
Yes ! Repair the Sensor ground shorted to the MAF Signal circuit.
Perform POWERTRAIN VERIFICATION TEST VER - 5.
No ! Go To 10
10.Turn the ignition off.
Disconnect the MAF Sensor harness connector.
Disconnect the PCM harness connector.
CAUTION: DO NOT PROBE THE PCM HARNESS CONNECTORS. PROBING
THE PCM HARNESS CONNECTORS WILL DAMAGE THE PCM TERMINALS
RESULTING IN POOR TERMINAL TO PIN CONNECTION. INSTALL
MILLER SPECIAL TOOL #8815 TO PERFORM DIAGNOSIS.
Measure the resistance of the Sensor ground circuit from the MAF Sensor harness
connector to the appropriate terminal of special tool #8815.
Is the resistance below 5.0 ohms?
Yes ! Go To 11
No ! Repair the open in the Sensor ground circuit.
Perform POWERTRAIN VERIFICATION TEST VER -5
11.NOTE: Before continuing, check the PCM harness connector terminals for
corrosion, damage, or terminal push out. Repair as necessary.
If there are no possible causes remaining, view repair.
Repair
Replace and program the Powertrain Control Module in accordance
with the Service Information.
Perform POWERTRAIN VERIFICATION TEST VER -5




Customer: replied 4 years ago.
Can you send me the procedure for replacing the Air Injection Pump on my 2005 Chrysler Sebring?
Expert:  Chad replied 4 years ago.
  1. Disconnect negative battery cable.
  2. Remove air inlet tube for the air cleaner box.
  3. Disconnect quick connect hose from the top of the air pump.
  4. Raise vehicle and support.
  5. Remove 3 mounting nuts.
  6. Unlock electrical connector.
  7. Unclip electrical connector from mounting bracket.
  8. Press tab and disconnect electrical connector.
  9. Disconnect quick connect hose from inlet of the air pump.
  10. Remove air pump from vehicle.

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Customer: replied 4 years ago.
Chad, in step 9 you mention the inlet port but you don't mention outlet port. My car has an outlet port, is this correct?
Expert:  Chad replied 4 years ago.
I can't remember at the moment. But if it does, it would be the only line still connected after doing the steps in the removal.
Those steps are straight from chrysler's site for removal of the pump.
Customer: replied 4 years ago.
Thank you.
Expert:  Chad replied 4 years ago.
Your Welcome.
Customer: replied 4 years ago.
Hi Chad, More questions...what is the input voltage to the air injection pump? Thanks.
Expert:  Chad replied 4 years ago.
It is a 12 volt supply from fuse 7 (40 amp) in the PDC, that feeds the air pump motor relay.

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Customer: replied 4 years ago.
Hi Chad, thank you for your help so far. After replacing the air injection pump, I cleared the CEL, but it is back on. Same Code, P0491: Secondary air injection system bank 1. What should I check next?
Expert:  Chad replied 4 years ago.
You will need to follow the diag procedure step by step that I posted for you. It is the post after the one you accepted.
Let me know the findings for each step after you take them.
Customer: replied 4 years ago.
Ok. Can you tell me what operational conditions the pump should run?
Expert:  Chad replied 4 years ago.
Operation....

The air injection system adds a controlled amount of air to the exhaust gases aiding oxidation of hydrocarbons and carbon monoxide in the exhaust stream. The system does not interfere with the ability of the EGR system (if used) to control nitrous oxide (NOx) emissions. Turns on only during a cold start.

Air is drawn into the pump through a rubber tube that is connected to the Mass Air Flow Sensor (MAF) and filter assembly. Airflow is measured by the MAF sensor. A voltage will be produced via the MAF sensor when air is passed through. This voltage correlates to airflow. The amount of voltage (airflow) will determine the amount of fuel that will be added to achieve the goal air/fuel ratio.

Air is then compressed by the air injector pump. It is expelled from the pump and routed into a rubber tube where it reaches the air pressure relief valve. Pressure relief holes in the relief valve will prevent excess downstream pressure. If excess downstream pressure occurs at the relief valve, it will be vented into the atmosphere.

Air is then routed through a tube, through the one-way check valves and injected into the catalytic convertors (referred to as downstream).

The one-way check valves protect the hoses, air pump and injection tubes from hot exhaust gases backing up into the system. Air is allowed to flow through these valves in one direction only (towards the catalytic convertors).

Downstream air flow assists the oxidation process in the catalyst, but does not interfere with EGR operation (if EGR system is used).

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