Body Control Modules: Other Nissan Altima L31

BCM FUNCTION

BCM has a combination switch reading function for reading the operation of combination switches (light, wiper washer and turn signal) in addition to the function for controlling the operation of various electrical components. See COMBINATION SWITCH READING FUNCTION . It also functions as an interface that receives signals from the A/C control unit (with manual A/C), A/C auto amplifier (with auto A/C), and sends signals to ECM using CAN communication.

Combination Switch Reading Function

Note. Each OUTPUT terminal transistor is activated at 10 millisecond interval. Therefore, after a switch is turned "ON", the electrical loads are activated with a time delay. But this time delay is so short that it cannot be noticed.

Note. Headlight has a dual system switch for safe operation.

The BCM reads combination switch (light, wiper washer, turn signal) status, and controls various electrical components according to the results. The BCM reads information of 20 switches and 5 diagnostic results by combining 5 output terminals (OUTPUT 1-5) and 5 input terminals (INPUT 1-5). (Scheme 19)

The BCM outputs battery voltage from input terminals (INPUT 1-5) all the time. At the same time output terminals (OUTPUT 1-5) activate transistors in turn, and allow current to flow. At this time, if any (1 or more) of the switches are "ON", the input terminals corresponding to these switches detect current flow, and BCM judges switches are "ON".

An example of this would be, when fog lamp switch is turned "ON", contact in combination switch turns "ON". At this time if OUTPUT 4 transistor is activated, BCM detects current flow in INPUT 5. When OUTPUT 4 transistor is "ON", BCM detects current flow in INPUT5, and judges fog lamp switch is "ON". Then BCM sends fog lamp "ON" signal to IPDM E/R using CAN communication. When OUTPUT 4 transistor is activated again, BCM detects current flow in INPUT 5, and confirms fog lamp switch is continuously "ON". (Scheme 20)

The BCM reads operation status of combination switches by the combination (Scheme 21)

Combination switch reading function has operation modes (Scheme 22) When BCM is not in sleep mode, each OUTPUT (1-5) terminal turns "ON-OFF" at 10 millisecond intervals. When BCM is in sleep mode, transistors of OUTPUT 1 and 2 stop the output, and BCM enters low-current-consumption mode. OUTPUTS (3-5) turn "ON-OFF" at 60 millisecond intervals, and receives lighting switch input only.

Scheme 19

Scheme 20

Scheme 21

Scheme 22

Can Communication Control

CAN communication is capable of dealing with a lot of information through the 2 communication lines (CAN L-line and CAN H-line) connecting control units in the system. Also each control unit functions to transmit and receive data, and reads necessary information only.

BCM Status Control

BCM changes its status depending on the operation status in order to save power consumption.

1. CAN Communication Status With ignition switch "ON", CAN communicates with other control units normally. Control by BCM is being operated properly. When ignition switch is "OFF", switching to sleep mode is possible. Even when ignition switch is "OFF", if CAN communication with IPDM E/R and combination meter is active, CAN communication status is active.
2. Sleep Status This is the status to stop CAN communication when ignition switch is turned "OFF", it transmits sleep request signal to IPDM E/R and combination meter. Two seconds after CAN communication with other control unit stops, it switches to CAN communication inactive status.
3. CAN Communication Inactive Status With ignition switch "OFF", CAN communication is not active. With ignition switch "OFF", control performed only by BCM is active. Two seconds after CAN communication with other control unit stops, it switches to CAN communication inactive status.
4. Sleep Status BCM is activated with low-current-consumption mode. CAN communication is not active. When CAN communication operation is detected, it switches to CAN communication status. When control performed only by BCM is required by switch, it shifts to CAN communication inactive mode. It changes combination switch reading function.

USING CONSULT-II

CONSULT-II can display each diagnostic item using the following diagnostic test modes: work support, self-diagnostic results, data monitor and active test through data reception and command transmission via the BCM communication line. (Scheme 23) Using (Scheme 24) diagnose items of each part.

Scheme 23

Scheme 24

Consult-II Inspection Procedure

1. With ignition switch "OFF", connect CONSULT-II to DLC and turn ignition "ON". see scheme 8
2. Touch "START".
3. Touch "BCM" on "SELECT SYSTEM" screen. (Scheme 25)
4. Select item to be diagnosed on "SELECT TEST ITEM" screen. (Scheme 26)

Scheme 25

Scheme 26

Detection Condition

BCM terminal No. 48 (Input 1) does not change. Open circuit in diagnosis 1 system line or open malfunction in output 1 transistor.

Possible Cause

Possible open in vehicle harness between BCM and combination switch, wiper switch and/or BCM.

BCM terminal No. 47 (Input 2) does not change. Open circuit in diagnosis 2 system line or open malfunction in output 2 transistor.

Vehicle harness between BCM and combination switch, wiper switch and/or BCM.

BCM terminal No. 46 (input 3) does not change. Open circuit in diagnosis 3 system line or open malfunction in output 3 transistor.

Vehicle harness between BCM and combination switch, wiper switch (front wiper LO, INT), lighting switch (Auto light) and/or BCM.

BCM terminal No. 45 (Input 4) does not change. Open circuit in diagnosis 4 system line or open malfunction in output 4 transistor.

Vehicle harness between BCM and combination switch, lighting switch and/or BCM.

BCM terminal No. 44 (Input 5) does not change. Open circuit in diagnosis 5 system line or open malfunction in output 5 transistor.

Vehicle harness between BCM and combination switch, lighting switch and/or BCM.

Headlight 1 switch "OFF", headlight 2 switch "ON".

Lighting switch.

Headlight 1 switch "ON", headlight 2 switch "OFF".

Lighting switch.

Possible Causes

Malfunction is detected when ECM can not communicate to other control unit, or ECM can not communicate for more than the specified time. Possible cause is

1. CAN communication line is open or shorted.

SYSTEM TESTS

Identify appropriate symptom, in SYMPTOM INDEX table, and perform appropriate test.

SYMPTOM INDEX

Vehicle harness shorted between BCM connector (M19), input terminal No. 1 and BCM output terminal No. 1, BCM and/or combination switch

Vehicle harness shorted between BCM input terminal No. 2 and BCM output terminal No. 2, BCM, and/or combination switch.

Vehicle harness shorted between BCM input terminal No. 3 and BCM output terminal No. 3, BCM and/or combination switch.

Vehicle harness shorted between BCM input terminal No. 4 and BCM output terminal No. 4, BCM and/or combination switch.

Vehicle harness shorted between BCM input terminal No. 5 and BCM output terminal No. 5, BCM and/or combination switch.

BODY CONTROL MODULE (BCM)

Information is not available from manufacturer.