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Home >> GMC >> 1991 >> Value Van 7.4 N >> Repair and Diagnosis >> External Pages >> Different car >> Section 43 (Engine Controls - Tests W/Codes - 8.0L) >> Self-Diagnostic Tests >> Test TC-11A - Left O2S Stays Below Center (Lean) (DTC 51)

Test TC-11A - Left O2S Stays Below Center (Lean) (DTC 51)

WARNING: This page is about a different car, the 1995 Dodge Pickup and 1995 Dodge Cab & Chassis. However, it is still accessible from the selected car via links, so may be relevant.
NOTE: For circuit and connector terminal identification, see CONNECTOR IDENTIFICATION  . For wiring diagrams, see WIRING DIAGRAMS  section at the end of this article.
NOTE: Scan tool displays dual O2S as LT O2S and RT O2S.
  1. Ensure fuel tank is at least 1/4 full. Low fuel level could set this trouble code. If vehicle ran out of fuel shortly before arriving for service, erase trouble codes. Perform TEST VER-2.
  2. If vehicle did not run out of fuel, check following components/systems for possible trouble code cause; ignition system failure, fuel pump/filter, fuel injectors, low fuel pressure, Manifold Absolute Pressure (MAP) sensor, O2S failure, vacuum leak, mechanical engine failure, faulty wiring or faulty connectors. Go to next step.
  3. Turn ignition off. Disconnect right O2S connector. Turn ignition on. Using scan tool, read LT O2S voltage. Wait for voltage reading to stabilize at 4.8-5.0 volts. Using scan tool, actuate fuel system while observing LT O2S voltage for 2 minutes. If voltage is not 4.8-5.0 volts, stop fuel system actuation. Go to step 7).
  4. If voltage is 4.8-5.0 volts, disconnect left O2S connector. Ensure scan tool is still actuating fuel system. Using scan tool in voltmeter mode, check voltage on left O2S connector, Auto Shutdown (ASD) relay output circuit (Dark Green/Orange wire). If voltage is less than 10 volts, repair open Dark Green/Orange wire. Perform TEST VER-2.
  5. If voltage is more than 10 volts, stop all actuator tests. Using an external ohmmeter, measure resistance of left O2S connector (sensor side), O2S heater element circuit between Black/White wire and Dark Green/Orange wire. If resistance is not 4-20 ohms, replace left O2S. Perform TEST VER-2.
  6. If resistance is 4-20 ohms, using scan tool in ohmmeter mode, check resistance of left O2S connector (harness side), heater ground circuit (Black/White wire). If resistance is more than 5 ohms, repair open Black/White wire. Perform TEST VER-2. If resistance is less than 5 ohms, replace left O2S. Perform TEST VER-2.
  7. Reconnect right O2S. Using scan tool, actuate fuel system. Inspect injectors for fuel leaks. Repair injectors as necessary. Perform TEST VER-2. If injectors are okay, stop fuel system actuation. Go to next step.
  8. Start engine. Check exhaust system between engine and left O2S for leaks. Repair exhaust as necessary. Perform TEST VER-2. If exhaust system is okay, turn ignition on with engine off. Go to next step.
  9. Inspect all related wiring and connectors. Repair as necessary. Perform TEST VER-2. If no problems are found in wiring or connectors, perform tests listed in LEFT OXYGEN SENSOR LEAN TESTS table, in sequence until problem is found.
LEFT OXYGEN SENSOR LEAN TESTS

Application Test
Fuel Pressure NTC-3A 
Ignition System NTC-2A 
Coolant Temperature Sensor NTC-4A 
MAP Sensor NTC-6A 
Mechanical Test NTC-18A 
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