- DS - RAM 500 PICKUP -.6L V6 V.V.T. P98-DOWNSTREAM FUEL TRIM SYSTEM LEAN BATTERY A0 0 87 87A RELAY- RUN/ START ASSEMBLY- POWER DISTRIBUTION CENTER FUSE A FUSE 78 0A CONNECTOR- STAR CAN C DASH 8 C CAN C (+) CAN C (-) A9 RD F9 PK/LG D7 TN/WT C D8 YL 9 8 9 8 96 FUSED B(+) O / O / 57 C FUSED IGNITION SWITCH OUTPUT (RUN-START) (UPSTREAM) CAN C (+) CAN C (-) O / O / 9 0 7 O / SUPPLY 8 O / 9 (DOWNSTREAM) O / O / 96 C MODULE- POWERTRAIN K99 BR/LG K DB/LB K90 BR/DG K DB/LG K99 BR/VT K99 BR/WT K DB/YL K90 DB/DG K DB K99 BR/GY (UPSTREAM) O / O / / (DOWNSTREAM) O / O / / O / O / (UPSTREAM) / O / SUPPLY O / (DOWNSTREAM) / 8009906 Theory of Operation The intent of this diagnostic is to identify rich or lean fuel system abnormalities which would cause vehicle emissions to exceed.5 times any of the standards. The base fuel feedback control will maintain the desired fuel/air mixture by modifying the injected fuel quantity according to the oxygen content of the exhaust gas. The Powertrain Control Module (PCM) makes short term and long term fuel corrections based on feedback from the Upstream Oxygen (O) Sensors.
The PCM monitors feedback from the Downstream O Sensors to determine and optimize the efficiency of the Catalytic Converters. The Upstream Fuel System Monitor and Downstream Fuel Trim Diagnostic monitors operate very differently; Upstream Fuel System Monitor The Upstream Fuel System Monitor diagnostic monitors the Upstream O Sensor feedback to determine the actual fuel/air ratio, which is then compared to the desired fuel/air ratio. The error between the two is measured and corrected for. This correction happens live and the instantaneous value of the correction is stored in short term fuel trim. Short term fuel trim is intended to correct temporary or dynamic errors in the air/fuel ratio. If the value of short term fuel trim is large enough for a sufficient period of time, it is assumed that whatever is causing the error is permanent and not temporary and the value in short term fuel trim is moved to long term fuel trim. When this transfer occurs, the short term fuel trim is re-zeroed and continues to look for temporary errors. If the combined value of the total fuel correction stored in short term and long term fuel trim (rich or lean) exceeds a calibrated threshold, for a calibrated period of time, a fuel system monitor fault is recorded. Downstream Fuel Trim Diagnostic A Downstream O Sensor goal voltage is selected to maintain the optimum catalyst efficiency. Corresponding Upstream O Sensor rich/lean switching point thresholds for various operating conditions are also selected which normally result in a Downstream O Sensor voltage close to this goal voltage. During normal operation, whenever the upstream rich/lean switching point threshold does not result in the desired downstream goal voltage, the downstream fuel trim feature trims (adjusts) the upstream rich/lean switching point threshold up or down appropriately until the desired downstream goal voltage is achieved. The amount of trim adjustment that is added or removed is called downstream fuel trim. If the trim adjustment to the Upstream O Sensor goes beyond a calibrated threshold (rich or lean), a fault is set. When Monitored and Set Conditions When Monitored: This diagnostic runs continuously when the following conditions are met: With the engine running in downstream closed loop fuel control. Battery voltage above.0 volts. Barometric pressure greater than 75 kpa. The ambient temperature above -7 C ( F). Fuel level greater than %. Altitude below 590.8 m (8500 ft.). Set Conditions: The value of the downstream fuel trim is compared with the lean thresholds. Every time the value exceeds the calibrated threshold, a fail timer increments and mass flow through the exhaust is accumulated. If the fail timer and accumulated mass flow exceed the fail thresholds, the test fails and the diagnostic stops running for that trip. It takes two consecutive failed trips to set a DTC. Default Actions: The MIL light will illuminate. EXHAUST SYSTEM LEAK Possible Causes
Possible Causes UPSTREAM O SENSOR WIRING ISSUE UPSTREAM O SENSOR DOWNSTREAM O SENSOR WIRING ISSUE DOWNSTREAM O SENSOR POWERTRAIN MODULE (PCM) Always perform the PRE-DIAGNOSTIC TROUBLESHOOTING PROCEDURE before proceeding. (Refer to 8 - DTC-Based Diagnostics/MODULE,. CHECK FOR AN ACTIVE DTC. With the scan tool, read DTCs and record on the repair order.. With the scan tool, record the related Freeze Frame data.. Using the recorded data along with the When Monitored and Set Conditions above, operate the vehicle in the conditions that set the DTC.. With the scan tool, read DTCs. Is the DTC active or pending? Yes Go To No Perform the INTERMITTENT CONDITION diagnostic procedure. (Refer to 8 - DTC-Based Diagnostics/ MODULE,. CHECK FOR OTHER DTCS. Refer to the recorded DTCs. Are there any O Sensor DTCs active or pending? Yes Perform the applicable diagnostic procedure(s). (Refer to 8 - DTC-Based Diagnostics/MODULE, Powertrain Control (PCM)/Diagnosis and Testing). No Go To. CHECK THE EXHAUST SYSTEM FOR LEAKS. Perform the CHECKING THE EXHAUST SYSTEM FOR LEAKS test procedure. (Refer to 9 - Non-DTC Diagnostics/Drivability - Gas - Diagnosis and Testing). NOTE: An exhaust leak of any size at or upstream of the Downstream O Sensor can cause this DTC to set. It is critical to thoroughly inspect and repair any leak before continuing on and replacing an O Sensor. Were any problems found? Yes Repair as necessary in accordance with the Service Information. No Go To
. CHECK THE UPSTREAM O SENSOR WIRING FOR AN OPEN OR SHORT TO NOTE: The Downstream Fuel Trim Diagnostic will fault based on the trim adjustment to the Upstream O Sensor being beyond a calibrated threshold. Therefore, if there are no exhaust system leaks, it is more likely that the Upstream O Sensor is the cause of any Downstream Fuel Trim System Rich/Lean fault than the Downstream O Sensor. For this reason the Upstream O Sensor and wiring should be diagnosed before the Downstream O Sensor.. Disconnect the Upstream O Sensor harness. Disconnect the PCM C harness 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 the GPEC Diagnostic Adaptor to perform the diagnosis.. Connect the Adapter, GPEC Diagnostic 06.. Check the Upstream O Sensor circuits; for a short to ground in the wiring between the O Sensor harness connector and the PCM C harness for an open or high resistance in the wiring between the O Sensor harness connector and the PCM C harness Were any problems found? Yes Perform the appropriate repair. No Go To 5 5. REPLACE THE UPSTREAM O SENSOR AND RETEST FOR DTC. Verify that there is good pin to terminal contact in the O Sensor / and Powertrain Control Module connectors. Replace the O Sensor / if no problems were found with the connectors. (Refer to - Fuel System/Fuel Injection/ SENSOR, Oxygen/Removal).. Reconnect all harness connectors.. With the scan tool, erase DTCs.. Using the recorded data along with the When Monitored and Set Conditions above, operate the vehicle in the conditions that set the DTC. 5. With the scan tool, read DTCs. Did the DTC return? Yes Go To 6 No Repair is complete. 6. CHECK THE DOWNSTREAM O SENSOR WIRING FOR AN OPEN OR SHORT TO. Disconnect the Downstream O Sensor harness
. Disconnect the PCM C harness 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 the GPEC Diagnostic Adaptor to perform the diagnosis.. Connect the Adapter, GPEC Diagnostic 06.. Check the Downstream O Sensor circuits; for a short to ground in the wiring between the O Sensor harness connector and the PCM C harness for an open or high resistance in the wiring between the O Sensor harness connector and the PCM C harness Were any problems found? Yes Perform the appropriate repair. No Go To 7 7. INSTALL A NEW DOWNSTREAM O SENSOR AND RETEST FOR DTC. Verify that there is good pin to terminal contact in the O Sensor / and Powertrain Control Module connectors. Install a new O Sensor / if no problems were found with the connectors. (Refer to - Fuel System/Fuel Injection/ SENSOR, Oxygen/Removal).. Reconnect all harness connectors.. With the scan tool, erase DTCs.. Using the recorded data along with the When Monitored and Set Conditions above, operate the vehicle in the conditions that set the DTC. 5. With the scan tool, read DTCs. Did the DTC return? Yes Go To 8 No Repair is complete. 8. CHECK RELATED HARNESS CONNECTIONS. Disconnect all PCM harness connectors.. Disconnect all related in-line harness connections (if equipped).. Disconnect the related component harness connectors.. Inspect harness connectors, component connectors, and all male and female terminals for the following conditions: Proper connector installation. Damaged connector locks. Corrosion. 5
Other signs of water intrusion. Weather seal damage (if equipped). Bent terminals. Overheating due to a poor connection (terminal may be discolored due to excessive current draw). Terminals that have been pushed back into the connector cavity. Check for spread terminals and verify proper terminal tension. Repair any conditions that are found. 5. Connect all PCM harness connectors. Be certain that all harness connectors are fully seated and the connector locks are fully engaged. 6. Connect all in-line harness connectors (if equipped). Be certain that all connectors are fully seated and the connector locks are fully engaged. 7. Connect all related component harness connectors. Be certain that all connectors are fully seated and the connector locks are fully engaged. 8. With the scan tool, erase DTCs. 9. Test drive or operate the vehicle in accordance with the when monitored and set conditions. 0. With the scan tool, read DTCs. Did the DTC return? Yes Replace and program the Powertrain Control Module (PCM) in accordance with the Service Information. (Refer to 08 - Electrical/8E - Electronic Control Modules/MODULE, Powertrain Control/Removal). No The wiring or poor connection problem has been repaired. 6