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Tahoe / Yukon Service Manual

DTC B1270 or B1271

Diagnostic Instructions Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Review Strategy Based Diagnosis for an overview of the diagnostic approach. Diagnostic Procedure Instructions provides an overview of each diagnostic category. DTC Descriptors DTC B1270 Left Side Object Detection LED Control DTC B1270 Right Side Object Detection LED Control For symptom byte information, refer to Symptom Byte List. Diagnostic Fault Information

Circuit Short to Ground Open/High Resistance Short to Voltage Signal Performanc
Left Side Object Detection LED Control Circuit B1270 92 B1270 92 B1270 92 B1270 92
Right Side Object Detection LED Control Circuit B1271 92 B1271 92 B1271 92 B1271 92

Circuit/System Description The side blind zone alert system sensors are located behind the rear fascia and detect and report objects on either side of the vehicle, within a specified blind zone. The system alerts with a visual indicator placed on each side rear view mirror, to the presence of objects that may not be visible in the inside rearview mirror and outside rearview mirrors. When the system detects a vehicle in the side blind zone while driving forward, independent if passing a vehicle or being passed, an amber warning symbol will light up in the appropriate outside mirror. This indicates that it may be unsafe to change lanes. If the driver then activates the turn signal, the amber warning symbol starts flashing and a chime sounds to give an extra warning not to change lanes. The side object sensor module communicates via serial data to the S79 Front Side Door Window Switch which provides the voltage to the outside rearview mirror to illuminate the side blind zone alert symbol on the mirror. Side blind zone alert is active from speeds of 10 km/h (6.2 MPH) up to 140 km/h (87 MPH). Driving faster deactivates the system, indicated by low lighting warning symbols in the mirrors. Driving under this speed again will turn off the warning symbols. If then a vehicle is detected in blind zone, the warning symbols will illuminate normally on the appropriate side. When the vehicle is started, both outside mirror displays will briefly come on to indicate that the system is operating. In vehicles equipped with Super Cruise (RPO UKL), the B218L Side Obstacle Detection Control Module - Left and B218R Side Obstacle Detection Control Module - Right are replaced by the B233SL Short Range Radar Rear Side Sensor - Left and B233SR Short Range Radar Rear Side Sensor - Right respectively. The system function remains the same. Conditions for Running the DTC Engine running. The Side blind zone alert is active from speeds of 10 km/h (6.2 MPH) up to 140 km/h (87  MPH). Conditions for Setting the DTC B1270 92 The module has detected a short to ground, short to voltage, or open in the left side object detection indicator circuit. B1271 02 The module has detected a short to ground, short to voltage, or open in the right side object detection indicator circuit. Action Taken When the DTC Sets The side blind zone alert system is inoperative and Service Side Detection System is displayed on the Driver Information Center. Conditions for Clearing the DTC The condition for setting the DTC is no longer present. Reference Information Schematic Reference Driver Assistance Systems Schematics Connector End View Reference Master Electrical Component List Description and Operation Side Blind Zone Alert Description and Operation Electrical Information Reference Circuit Testing Connector Repairs Testing for Intermittent Conditions and Poor Connections Wiring Repairs Scan Tool Reference Control Module References for scan tool information Special Tools EL-35616-210 Test Light – Probe Kit Circuit/System Verification

  1. Ignition OFF, ignition ON.
  2. Verify the side blind zone alert system indicators located in the outside rearview mirrors briefly turn ON and then OFF during the system self test when ignition is turned ON. ⇒ If the side blind zone alert system indicators do not briefly turn ON and OFF Refer to Circuit/System Testing ⇓ If both side blind zone alert indicators briefly turn ON and OFF
  3. All OK. Circuit/System Testing
  1. Ignition OFF and all vehicle systems OFF, disconnect the in-line harness connector for the appropriate A9 Outside Rearview Mirror. It may take up to 2 min for all vehicle systems to power down. Driver Door Harness to Outside Rearview Mirror Passenger Door Harness to Outside Rearview Mirror
  2. Test for less than 10 Ω between the ground circuit terminal 9 and ground. ⇒ If 10 Ω or greater 2.1. Ignition OFF. 2.2. Test for less than 2 Ω in the ground circuit end to end. ⇒ If 2 Ω or greater, repair the open/high resistance in the circuit. ⇒ If less than 2 Ω, repair the open/high resistance in the ground connection. ⇒ If less than 10 Ω
  3. Ignition ON, connect a test lamp between the control circuit terminal 4 and the ground circuit terminal 9.
  4. Verify the test lamp turns ON and OFF when commanding the Object Detection Alert Indicators On and Off with a scan tool. ⇒ If the test lamp is always OFF 4.1. Ignition OFF, disconnect the harness connector at the appropriate S79 Front Side Door Window Control Switch. 4.2. Test for infinite resistance between the control circuit and ground. ⇒ If less than infinite resistance, repair the short to ground on the circuit. ⇓ If infinite resistance 4.3. Test for less than 2 Ω in the control circuit end to end. ⇒ If 2 Ω or greater, repair the open/high resistance in the circuit. ⇒ If less than 2 Ω, replace the S79 Front Side Door Window Control Switch. ⇒ If the test lamp is always ON 4.1. Ignition OFF, disconnect the harness connector at the S79 Front Side Door Window Control Switch, ignition ON. 4.2. Test for less than 1 V between the control circuit and ground. ⇒ If 1 V or greater, repair the short to voltage on the circuit. ⇒ If less than 1 V, replace the S79 Front Side Door Window Control Switch. ⇓ If the test lamp turns ON and OFF
  5. Test or replace the A9 Outside Rearview Mirror Glass. Repair Instructions Perform the Diagnostic Repair Verification after completing the repair. Outside Rearview Mirror Glass Replacement Front Side Door Window Control Switch Replacement Control Module References for control module replacement, programming and setup