SPN 3227 or Suspect Parameter Number (SPN) and Failure Mode Indicator (FMI) Description

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Lisa Preston
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1 SPN 3227 or 3266 Suspect Parameter Number (SPN) and Failure Mode Indicator (FMI) Description SPN FMI Description Possible Causes EGO Bank A Sensor 2 Open or short to ground on Voltage Low signal circuit Open or high resistance on low reference circuit Malfunctioning EGO heater or sensor EGO Bank A Sensor 2 Voltage High EGO Bank B Sensor 2 Voltage Low EGO Bank B Sensor 2 Voltage High Short to voltage on signal circuit Malfunctioning EGO sensor Open or short to ground on signal circuit Open or high resistance on low reference circuit Malfunctioning EGO heater or sensor Short to voltage on signal circuit Malfunctioning EGO sensor Circuit Description The post-catalyst EGO sensors are used for catalyst efficiency. Each EGO sensor compares the oxygen content of the air around the sensor with the oxygen content in the exhaust system. The engine control module (ECM) calculates the air fuel ratio in Open Loop mode when the engine is started. As the EGO sensors heat up they generate voltage in the range of mv. When the ECM receives continuous voltage signals from the EGO sensors the ECM will enter a Closed Loop mode. An EGO sensor voltage that increases toward 1000 mv

2 indicates a rich mixture and an EGO voltage that decreases toward 0 mv indicates a lean mixture. A heater element inside the EGO sensors is used to decrease the time required to meet closed loop operating conditions. Conditions to Run SPN The SPN runs continuously when in Closed Loop operation. Conditions to Set SPN SPN EGO Bank A Sensor 2 Voltage Low The ECM detects that the EGO signal is less than 50 mv for greater than 60 seconds. SPN EGO Bank A Sensor 2 Voltage High The ECM detects that the EGO signal is greater than 1.2 V for greater than 240 ms. SPN EGO Bank B Sensor 2 Voltage Low The ECM detects that the EGO signal is less than 50 mv for greater than 60 seconds. SPN EGO Bank B Sensor 2 Voltage High The ECM detects that the EGO signal is greater than 1.2 V for greater than 240 ms. Action Taken When SPN Sets SPN EGO Bank A Sensor 2 Voltage Low is a Type B SPN SPN EGO Bank A Sensor 2 Voltage High

3 is a Type B SPN SPN EGO Bank B Sensor 2 Voltage Low is a Type B SPN SPN EGO Bank B Sensor 2 Voltage High is a Type B SPN Diagnostic Reference Review Strategy Based Diagnosis for an overview of the diagnostic approach. Diagnostic Procedure Instructions provides an overview of each diagnostic category. Perform the Diagnostic System Check prior to using this diagnostic. Test for intermittent or poor connections. Review Schematics and Connector End Views to locate test points. Review the SPN Type, Indicator Lamp Definitions, and Conditions to Clear the SPN/Indicator Lamp. Diagnostic Tips Check for vacuum leaks. Check for restrictions in the air inlet and exhaust systems. Verify the engine is not misfiring. Test for intermittent or poor connections. Verify the fuses are good.

4 Required Tools Terminal Test Probe Kit Fused Jumper Digital Multi-meter High Impedance Test Lamp Electronic Service Tool Circuit Diagnostics WARNING! To prevent bodily injury or death, stay away from hot engine surfaces and rotating engine components. 1. Ignition OFF, disconnect the appropriate EGO sensor, verify less than 10 Ω between the EGO harness connector low reference circuit terminal A and ground. If greater than 10 Ω, disconnect the ECM connector J1-B, test for less than 5 Ω between EGO connector low reference circuit terminal A and the appropriate ECM terminal listed below: J1-B terminal J3 = EGO Bank A Sensor 1 J1-B terminal J4 = EGO Bank B Sensor 1 If 5 Ω or greater, repair the open or high resistance in the circuit. If less than 5 Ω, replace the ECM. If less than 10 Ω, go to Step 2 2. Ignition ON, verify the appropriate Electronic Service Tool O2 parameter is between -10% and 18%. If less than -10%, ignition OFF, disconnect the ECM harness connector J1-B, test for infinite resistance between the appropriate EGO signal circuit and ground. If not infinite resistance, repair the short to ground in the circuit.

5 If infinite resistance, test for less than 5 Ω between the harness connector of the appropriate EGO signal circuit terminal A and the appropriate ECM J1-B terminal listed below: J1-B terminal K3 = EGO Bank A Sensor 1 J1-B terminal K4 = EGO Bank B Sensor 1 a) If greater than 5 Ω, repair the open/high resistance in the circuit. b) If less than 5 Ω, replace the ECM. If greater than 18%, ignition OFF, disconnect the ECM harness connect J1-B, ignition ON, test for less than 1 V between the EGO harness connector terminal A and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the ECM. If between -10% and 18%, go to step 3 3. Connect a 3 A fused jumper between the appropriate EGO signal circuit terminal B and the low reference circuit terminal A, Verify the appropriate Electronic Service Tool O2 parameter is less than -10%. If -10% or greater, ignition OFF, remove fused jumper, disconnect the ECM connector J1-B, test for less than 5 Ω between the EGO signal circuit and the appropriate ECM J1-B terminal listed below: J1-B terminal K3 = EGO Bank A Sensor 1 J1-B terminal K4 = EGO Bank B Sensor 1 If 5 Ω or greater, repair the open/high resistance in the circuit. If less than 5 Ω, replace the ECM. If less than -10%, replace the appropriate EGO sensor.

SPN 51 or Suspect Parameter Number (SPN) and Failure Mode Indicator (FMI) Description

SPN 51 or Suspect Parameter Number (SPN) and Failure Mode Indicator (FMI) Description SPN 51 or 3673 Suspect Parameter Number (SPN) and Failure Mode Indicator (FMI) Description SPN FMI Description Possible Causes 51 3 TPS1 Sensor Signal Voltage High Open/high resistance in low Short to