Q501 4 Cylinder MT Application DTC Troubleshooting Data Version: 0.1 Date: 21-Sep-2018 Prepared By: Mithi Prasad, Sarang Kulkarni, Manish Gupta Checked By: Yogesh Jadhav Approved By: Satish Kumar P Page: 940 of 1052 Copyright © TATA MOTORS Ltd. This document must not be used in any way, such as copying and redistributing to third parties, without the consent of author. P1275-4B: Over Temperature of the power stage for AC compressor – Over Temperature of the power stage for AC compressor Overview: DTC Description (User Friendly) Over Temperature of the power stage for AC compressor ECU Pin Number K090 Customer Symptom MIL OFF, CEL ON. Vehicle cabin will not be cooled even after AC is turned ON. Fault Effects (On Vehicle) AC Will not work (Cabin Cooling will not happen). Lamp Status (If Any) CEL ON. CEL Turns Off as and when fault condition is not present / healed. Fault Detection Condition (Root cause) The hardware detects an over temperature error on the digital output power stage for the actuator (K090). Normal Operating Condition No Fault Probable Trouble Area Check, whether there is dis-continuity in wiring harness between AC Relay and EMS ECU. Check for ECM pin K090 is SC to Battery AC Relay faulty, EMS ECU faulty Healing Condition Rectify the error Clear through diagnostic tool Ignition OFF & ON Component Details: AC Compressor has a magnetic Clutch; EMS ECU energizes Coil of the magnetic clutch. After being energized, Clutch engages the compressor to the EMS ECU. Preliminary Checks: 1. Check whether the customer voice / view about the issue is matching with the fault effects mentioned in above Table. If yes, go ahead with next steps. If not, check for other DTC’s presence. 2. Check whether other customers report similar complaints earlier. If yes, perform the preliminary checks with respect to earlier issue closure.\ 3. Check, whether the AC is functional, if AC is not functional, then check the wiring harness connections between EMS ECU and AC Relay. 4. Loose/ Damaged Connections between AC Compressor Relay and EMS ECU. 5. Loose/ Damaged Connections between AC Compressor Relay and Battery supply or Ground. 6. Check for proper installation of AC relay in fuse box. 7. Check for damage of pins at ECU connector. Trouble Shooting: Step Checks IF YES IF NO 1 Check for any mechanical damage in AC Relay Replace faulty Relay Go to next step 2 Is there wiring harness electrical continuity between ECU pin 48 & AC relay pin 3. Also Check continuity between the Main Relay supply and the AC relay pin 1. Also check continuity from AC Relay pin 1 to GND. Go to next step Rectify the wiring harness connections as per the circuit schematic.
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