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Check reference values between ECM terminals and ground under the following conditions: ECM TERMINAL NO. ITEM CONDITION DATA (DC VOLTAGE) 18 Upstream oxygen sensor • Engine is running • Warm-up condition • Keep the engine speed Approximately 0.1 - 0.9 V (change 5 - 8 times in 10 seconds periodically) 28 Downstream oxygen sensor heating - - 36 Sensor (GND) • Warm-up condition • Idle speed Approximately 0 V 48 Upstream oxygen sensor heating - - 55 Downstream oxygen sensor • Engine is running • Warm-up condition • Keep the engine speed Approximately 100 mV On Board Diagnostic Logic DTC NO. DTC DEFINITION DTC DETECTION CONDITION POSSIBLE CAUSE P0031 O 2 sensor 1 heater control circuit low Engine is running • Fuel quality • Upstream O 2 sensor • Harness or connectors • ECM DTC Confirmation Procedure: Before performing the following procedure, confirm that battery voltage is more than 12 V. • Turn ignition switch off. • Connect the X-431 scan tool to the Data Link Connector (DLC) - use the most current software available. • Turn ignition switch on and record and erase DTC. • Start engine and warm it up to the normal operating temperature. • Turn ignition switch off and wait at least 10 seconds. • Start engine and keep the engine speed 2000 RPM for at least 1 minute. • Let engine idle for 2 minutes, select view DTC and data stream. • If the DTC is detected, the DTC condition is current. Go to Diagnostic Procedure - Step 1. • If the DTC is not detected, the DTC condition is intermittent (See Diagnostic Help and Intermittent DTC Trou- bleshooting in Section 03 Electronic Engine Controls for more information. NOTE : DIAGNOSIS & TESTING 03
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