Vehicle Platform & ECU Name DTC Troubleshooting Data Ver: 1 Date: 23/11/2022 Author: ERC Page 522 of 834 Copyright by TATA MOTORS Ltd. This document must not be used in any w ay, such as copying and redistributing to third parties, w ithout our consent P0646-00: Air conditioning relay control – circuit short to ground Overview: DTC Code P0646-00 DTC Description as per ISO standard AC Clutch Relay Control Circuit Low ECU Pin Number B71 Customer Symptom AC Compressor will be continuously engaged irrespective of AC Request which will reduce the fuel efficiency. Fault Effects (On Vehicle) AC Compressor will be continuously engaged. Lamp Status (If Any) CE lamp is on Fault Detection Condition This fault gets logged if the AC Clutch control pin of EMS ECU is short circuited to ground. Normal Operating Condition Healthy wiring harness connections between AC Relay and EMS ECU Probable Trouble Area AC Clutch relay Related wiring Harness, connector or terminals ECU Component Details: AC Compressor has a magnetic Clutch; Coil of the magnetic clutch is energized by EMS ECU. After getting Energized, Clutch engages the compressor to the EMS ECU. Preliminary Checks: Check whether the customer voice / view about the issue is matching with the fault effects mentioned above. If yes, go ahead with next steps. If not, check for other DTC’s presence. Check whether similar complaints are earlier reported. If yes, perform the preliminary checks with respect to earlier issue closure. Loose/ Damaged Connections between AC Compressor Relay and EMS ECU. Loose/ Damaged Connections between AC Compressor Relay and Battery supply or Ground. Check for proper installation of AC relay in fuse box. Check for damage of pins at ECU connector. Trouble Shooting: Step Checks IF YES IF NO 1. Are Relay Contacts weld / Stuck Open Replace the Relay Go to Step 2 2. Is there wiring harness electrical continuity between i. ECU pin B71 & AC relay pin 86(coil input) ii.Supply through Main Relay and the AC relay pin 85. iii. AC Relay pin 30 to battery supply. Go to Step 3 Establish continuity by rectifying harness connections as per
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