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Fuel Composition Sensor

NOTE: Fuel composition sensor is only used on models equipped with a flex-fuel 5.3L (RPO code L59).
NOTE: A malfunction in Fuel Composition (FC) sensor circuit can set a Diagnostic Trouble Code (DTC). For testing procedures and specifications, perform appropriate diagnostic test. See DIAGNOSTIC TROUBLE CODE DEFINITIONS in appropriate SELF-DIAGNOSTICS article.
  1. Perform an accuracy test of Fuel Composition Tester (J 44175). Fill tester with acetone. Connect DMM to tester terminals. Set DMM to AC hertz scale and take a reading. Is reading 130-142 Hz? If yes, go to next step. If no, go to step  7.
    2. NOTE: Drain acetone completely from tester. Clean beaker with a clean dry paper towel before taking a fuel sample. Be careful not to allow fingerprints, sweat, water or any other outside debris contaminate fuel sample, beaker, tester or fuel gauge as this will cause an error in test result, leading to a misdiagnosis.
  2. Perform a fuel test using fuel composition tester. Install a fuel pressure gauge into service port located on rear of injector rail. Start engine and open valve on pressure gauge. Allow enough fuel to pass through gauge to flush any previous fuel from inside hose. Draw fuel from fuel pressure gauge into beaker supplied with test kit. Transfer fuel from beaker into fuel tester. Turn ON fuel tester and note Red and Green LED. Is Green LED ON? If yes, go to step  4. If no, go to next step.
  3. Is Red LED ON? If yes, go to step  5. If no, go to step  7.
  4. Connect DMM to fuel tester terminals. Set DMM to AC Hz scale and take a reading of fuel sample. Start engine and monitor fuel composition frequency on scan tool. Is reading from scan tool and DMM within 12 Hz? If yes, system is okay. If no, go to step  6.
  5. The fuel is contaminated. Drain fuel from tank. Replace fuel. Is action complete? If yes, system is okay.
  6. Replace fuel composition sensor. Is action complete? If yes, system is okay.
  7. Replace 9-volt battery and retest. If result is the same, tester will need to be sent out for repair.
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