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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: 322 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.
P0686 - 94: Main relay command (unexpected operation) – Unexpected Operation
DTC Description as per ISO standard
Main relay command – Unexpected operation
ECU Pin Number
K88,K01,K03,K05 (supply after main relay)
Customer Symptom
MIL ON
Fault Effects (On Vehicle)
Vehicle may not start
Lamp Status (If Any)
MIL ON1 (Lamp turn On immediately when fault detected)
Fault Detection Condition (Root cause)
Ignition ON
Normal Operating Condition
Fault condition no more present
Probable Trouble Area
1. Check the other DTCs
2. Main relay circuit open intermittently
3. EMS ECU.
Healing Condition
1. Run the diagnostic procedures to check the ECU Power &
ground.
2. Check Supply after main relay
3. Clear the DTC.
4. Read the DTC once again.
Component Details:
EMS ECU is an electronic controller which controls the Engine functionality by interfacing with various sensors, actuators
And other controllers (via CAN).
Preliminary Checks:
1. Check whether the customer voice / view about the issue is matching with the fault effects mentioned above.
2. If yes, go ahead with next steps. If not, check for other DTC’s presence.
3. Check whether similar complaints are earlier reported. If yes, perform the preliminary checks with respect to
4. Earlier issue closure. Check for pin back out at EMS ecu connector.
5. Check whether the EMS is receiving Battery supply and Ground
6. Check whether the Battery is healthy.