EDI DIAGNOSIS SERVICE MANUAL NUMBER 22
Page 5E-52 90-860074--1 FEBRUARY 2002
Glow Plug Auxiliary Relay, If Equipped
Scan Code: P1640
Blink Code: No recognition by ECM.
Malfunction Indicator Lamp: OFF
ECM
50
BLU/BLK
75476
3
BLK/YEL
86
30
87
8630
87
85
BRN
BLU/YEL
RED
RED
BRN
BRN
BLK
BLU/YEL
85
a
b
c
d
f
e
g
b
87
85
BLU/BRN
BLU/TAN
a-Engine Main Relay
b-Circuit Breaker
c-Glow Plug Main Relay
d-Glow Plug Auxiliary Relay
e-Engine Harness Connector
f-16 Terminal Instrument Harness Connector
g-To Glow Plug Lamp
CIRCUIT DESCRIPTION:
The Glow Plug Main Relay (or Actuator) and the Glow Plug Auxiliary Relay are inside the
electrical box of the engine. The ECM determines if, when and for how long a period the glow
plugs (relays) should be activated based on coolant temperature information from the ECT.
This processing by the ECM is done before, during and after the engine is started. It is the
relay that controls the large amount of amperes needed by the glow plugs. Concurrent with
supplying power to half of the glow plugs the Glow Plug Relay Actuator relay activates the
Glow Plug Auxiliary Relay. The Auxiliary Relay’s coil is energized closing a switch which
thereby supplies current to the remaining glow plugs.
The ECM closes a ground path circuit for the Glow Plug Lamp whenever the system is
operating.
A failure in the Glow Plug Auxiliary Relay circuit should set a Scan Code P1640.
CKT PIN
NAME
50 ECM controlled Glow Plug Relay Ground (–)
3 ECM controlled Ground (–) for dash panel Glow Plug Lamp
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