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Home › Jeep › 1998 › Cherokee Limited, 2.5 P › Repair and Diagnosis › Engine Performance › System › Engine Controls - Tests W/Codes - Engine Performance › Self-Diagnostic Tests › Test TC-121A: Fuel System 2/1 Lean

Test TC-121A: Fuel System 2/1 Lean

NOTE: This test applies to AN body (2WD) equipped with 5.9L engine, and BE/BR bodies equipped with 5.9L heavy-duty engine or 8.0L engine only. For connector terminal identification, see CONNECTOR IDENTIFICATION . For component location and wiring diagram, see WIRING DIAGRAMS article.
NOTE: Very low fuel level could cause FUEL SYSTEM LEAN DTC to set. Ensure fuel tank is at least 1/4 full.
  1. If vehicle ran out of fuel shortly before FUEL SYSTEM LEAN DTC set, ensure fuel tank is at least 1/4 full. Using scan tool, erase DTCs and perform TEST VER-5A: ROAD TEST FOR OBD-II TROUBLE CODES . If vehicle did not run out of fuel shortly before DTC sets, ensure fuel tank is at least 1/4 full and go to next step.
  2. FUEL SYSTEM LEAN DTC sets if Powertrain Control Module (PCM) senses fuel system is running too lean on 2 sequential trips. Possible causes are: defective ignition coil, defective PCM, engine wear, defective exhaust manifold, defective fuel pump, defective fuel filter, defective ignition secondary wires, defective injectors, defective MAP sensor, defective upstream Heated Oxygen Sensor (HO2S), defective fuel pressure regulator, defective fuel pump relay, defective spark plugs, or defective connector terminals or connector wires. Go to next step.
  3. Using scan tool, read DTCs. Repair any other DTCs before proceeding. See DTC MESSAGES & CODES  table in DTC TEST and perform appropriate test(s). If no other DTCs exist, go to next step.
  4. Check if any Technical Service Bulletins (TSBs) apply to vehicle. If a TSB exists, perform corrective action and perform TEST VER-5A: ROAD TEST FOR OBD-II TROUBLE CODES . If no TSBs exist, go to next step.
  5. Start engine. Allow engine to reach normal operating temperature. Allow engine to idle for 20 seconds after warm-up. Inspect exhaust system between engine and upstream HO2S for leaks. Repair exhaust system as necessary and perform TEST VER-5A: ROAD TEST FOR OBD-II TROUBLE CODES . If exhaust system is okay, go to next step.
  6. Using scan tool, monitor 2/1 O2 SENSOR state for at least 20 seconds. If state is switching between LEAN-CENTER-LEAN 2 or more times in 20 seconds, condition required to set DTC is no longer present. Test is complete. Perform TEST VER-5A: ROAD TEST FOR OBD-II TROUBLE CODES . If state does not switch as specified, go to next step
  7. Using scan tool, read LONG TERM ADAPTIVE MEMORY value. If value is not 20-32 percent, condition required to set DTC is no longer present. Test is complete. Perform TEST VER-5A: ROAD TEST FOR OBD-II TROUBLE CODES . If value is as specified, perform TEST TC-121B: FUEL SYSTEM 2/1 LEAN .
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