P1438

2UR-FSE ENGINE CONTROL SYSTEM: SFI SYSTEM: P1438: HCAC System Variable Valve Circuit Low

DTC P1438 - HCAC System Variable Valve Circuit Low

DESCRIPTION

The Hydro-Carbon Adsorber and Catalyst (HCAC) system is used to reduce the amount of HC in the exhaust emissions. In this system, the HC adsorber absorbs HC of the exhaust emissions when the catalyst is cold, and the catalyst purges the absorbed HC after the catalyst is warmed up.
The HCAC VSV is supplied with the battery voltage (12 V). When the internal transistor of the ECM turns on, the HCAC VSV opens.
When the catalyst is cold, the engine control module (ECM) turns on the HCAC VSV. The intake manifold pressure (vacuum) is applied to the HCAC actuator, and it opens the HCAC valve. The exhaust emissions flow to the HC adsorber.
After the catalyst is warmed up, the ECM turns off the HCAC VSV. The HCAC valve is opened by the return spring of the HCAC actuator. The exhaust emissions flow to the catalyst.






MONITOR DESCRIPTION

There is a HCAC VSV monitoring circuit in the ECM. The monitoring circuit voltage becomes lower when the HCAC VSV is turned on, and it becomes higher when the HCAC VSV turns off.
If the monitoring circuit voltage is low when the HCAC VSV turns off, the ECM interprets this as a malfunction. The ECM illuminates the malfunction indicator lamp (MIL) and sets the diagnosis trouble code (DTC).

MONITOR STRATEGY





TYPICAL ENABLING CONDITIONS





TYPICAL MALFUNCTION THRESHOLDS





WIRING DIAGRAM





INSPECTION PROCEDURE

PROCEDURE

1. CHECK HCAC VSV (POWER SOURCE)





(a) Disconnect the HCAC VSV connector.
(b) Turn the power switch ON (IG).
(c) Measure the voltage according to the value(s) in the table below.
Standard voltage:






NG -- INSPECT FUSE (EFI AND EFI MAIN NO. 1)
OK -- Continue to next step.
2. INSPECT HCAC VSV
(a) Inspect the HCAC VSV Testing and Inspection.
NG -- REPLACE HCAC VSV
OK -- Continue to next step.
3. CHECK HCAC VSV (POWER SOURCE)





(a) Connect the HCAC VSV connector.
(b) Turn the power switch ON (IG).
(c) Measure the voltage according to the value(s) in the table below.
Standard voltage:






NG -- CHECK HARNESS AND CONNECTOR (HCAC VSV - ECM)
OK -- REPLACE ECM
4. CHECK HARNESS AND CONNECTOR (HCAC VSV - ECM)





(a) Disconnect the E57 HCAC VSV connector.
(b) Disconnect the A13 ECM connector.
(c) Measure the resistance according to the value(s) in table below.
Standard resistance:






NG -- REPAIR OR REPLACE HARNESS OR CONNECTOR
OK -- REPLACE ECM
5. INSPECT FUSE (EFI AND EFI MAIN NO. 1)





(a) Remove the EFI and EFI MAIN2 fuses from the engine room No. 2 junction block.
(b) Measure the resistance according to the value(s) in the table below.
Standard resistance:






NG -- CHECK FOR SHORT IN ALL HARNESSES AND CONNECTORS CONNECTED TO FUSE AND REPLACE FUSE
OK -- Continue to next step.
6. INSPECT EFI RELAY (EFI MAIN2)
(a) Inspect the EFI MAIN2 relay EFI Relay.
NG -- REPLACE EFI MAIN2 RELAY
OK -- REPAIR OR REPLACE HARNESS OR CONNECTOR (HCAC VSV - BATTERY)