P2099-DOWNSTREAM FUEL TRIM SYSTEM 2 RICH





For a complete wiring diagram Refer to Section 8W.



Possible Causes
EXHAUST LEAK
ENGINE MECHANICAL
2/2 O2 SENSOR
(K342) O2 SENSOR 2/2 SIGNAL CIRCUIT
(K399) O2 SENSOR 2/2 HEATER CONTROL CIRCUIT
(K904) O2 RETURN DOWNSTREAM CIRCUIT
FUEL CONTAMINATION

Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING).



Diagnostic Test

1. ACTIVE DTC

NOTE: Check the vehicle repair history. If the 2/2 O2 has been replaced make sure that the O2 sensor was properly installed and meets OEM specification.

NOTE: Check for contaminants that may have damaged the O2 Sensor: contaminated fuel, unapproved silicone, oil and coolant.


Start the engine.
Allow the engine to reach normal operating temperature.
With a scan tool, select View DTCs.

NOTE: It may be necessary to drive the vehicle to meet the conditions to set this DTC, try to repeat the conditions in which the fault originally set by reviewing the Freeze Frame data.



Is the DTC Active or Pending at this time?

Yes


No

2. CHECKING THE EXHAUST SYSTEM FOR LEAKS

Turn the ignition off.
Raise the vehicle in accordance with the Service Information.

WARNING: The normal operating temperature of the exhaust system is very high. Never work around or attempt to service any part of the exhaust system until it has cooled. Special care should be taken when working near the catalytic converter. The temperature of the converter rises to a high level after a short period of engine operating time


Connect Exhaust Cone #8404-EC or #8404–EC to Air Pressure Regulator (with hose) #W-18-MIL-1146AS.

CAUTION: The air pressure must not exceed 27.6 kPa (4 psi), otherwise engine damage can occur.


Attach shop air to the air pressure regulator.
Adjust the Air Pressure Regulator to 27.6 kPa (4 psi)
Insert the exhaust cone into the vehicle tail pipe.
If the vehicle is equipped with dual exhaust. Use the #8404-ECT with equipped attached plug, plug one side of the dual exhaust pipe. Pressurize the other as described above.
Apply SNOOP leak finder liquid or a mixture of liquid dish soap and water to the following areas:
- All welded joints from the exhaust manifold to 152.4 mm (6 inches) behind the downstream O2 sensor
- O2 sensor seal points
- O2 sensor boss welds
- Flange/joint connection(s)
- Exhaust manifold to cylinder head connection(s)
- EGR solenoid gasket base and tube seal points (if equipped)
Watch for the liquid/soapy water to bubble.
Use the following definitions to help determine if system or component repair/replacement is necessary:
Type 1 Leak is defined as a leak where very small foam like bubbles 1 mm (0.04 of an inch) or less appear.
Any Type 1 or greater leaks found in welded joints, O2 sensor seal points or O2 sensor boss welds must be repaired or the component must be replaced.
Type 2 Leak is defined as a leak where larger bubbles pea size, 8 mm (0.3 of an inch) or greater appear.
Any Type 2 or greater leaks found in flange or joint connections, exhaust manifold to cylinder head connections, or EGR gasket and tube seal points must be repaired or the components must be replaced

Leak Location
Repair required if results at 27.6 kPa (4 psi) reveal bubble size:
Welded joints
 		Type 1, 1 mm (0.04 of an inch) or greater
O2 Sensor seal points
 		Type 1, 1 mm (0.04 of an inch) or greater
O2 Sensor boss welds
 		Type 1, 1 mm (0.04 of an inch) or greater
Flange / joint connections
 		Type 2, 8 mm (0.3 of an inch) or greater
Exhaust Manifold to cylinder head connections
 		Type 2, 8 mm (0.3 of an inch) or greater
EGR gasket and tube seal points
 		Type 2, 8 mm (0.3 of an inch) or greater


If a leak is found that matches the above definition, repair or replace the component as necessary.
Once the repair is complete, repeat the procedure to verify that all leaks have been repaired.

Were any exhaust leaks found?

Yes


No

3. ENGINE MECHANICAL

Check for any of the following conditions/mechanical problems.
AIR INDUCTION SYSTEM - must be free from leaks
ENGINE VACUUM - must be at least 13 inches in neutral
ENGINE VALVE TIMING - must be within specifications
ENGINE COMPRESSION - must be within specifications
ENGINE EXHAUST SYSTEM - must be free of any restrictions or leaks
ENGINE PCV SYSTEM - must flow freely
TORQUE CONVERTER STALL SPEED - must be within specifications
POWER BRAKE BOOSTER - no internal vacuum leaks
FUEL - must be free of contamination
FUEL INJECTOR - plugged or restricted injector; control wire not connected to correct injector

Are there any engine mechanical problems?

Yes


No

4. O2 SENSOR



Ignition on, engine not running.
Disconnect the 2/2 O2 Sensor harness connector.
With the scan tool, monitor the 2/2 O2 Sensor voltage.
The O2 Sensor voltage should read 5.0 volts on the scan tool with the connector disconnected.
Using a jumper wire, jump the (K243) O2 Signal 2/2 circuit to the (K904) O2 Return Downstream circuit in the O2 Sensor harness connector.

NOTE: The voltage should drop from 5.0 volts to 2.5 volts with the jumper wire in place.



Did the O2 Sensor volts change from 5.0 volts to 2.5 volts?

Yes


No

5. (K243) O2 SENSOR 2/2 SIGNAL CIRCUIT

Remove the jump wire.
Ignition on, engine not running.
With the scan tool, monitor the 2/2 O2 Sensor voltage.

Is the voltage above 4.8 volts?

Yes


No

6. (K399) O2 SENSOR 2/2 HEATER CONTROL CIRCUIT OPEN



Turn the ignition off.
Disconnect the C3 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 (K399) O2 Sensor 2/2 Heater Control circuit from the O2 Sensor harness connector to the appropriate terminal of special tool #8815.

Is the resistance below 5.0 ohms?

Yes


No

7. (K904) O2 RETURN DOWNSTREAM CIRCUIT



Measure the voltage on the (K904) O2 Return Downstream circuit in the O2 Sensor harness connector.

Is the voltage at 2.5 volts?

Yes


No