DTC P1646 Evaporative Emission (EVAP) Vent Solenoid Control Circuit. Cadillac DeVille 1998

For 1990-2009 cars only

Makes 🢒 Cadillac 🢒 1998 🢒 DeVille 🢒 Engine 🢒 Engine Controls - 4.0L and 4.6L 🢒 DTC P1646 Evaporative Emission (EVAP) Vent Solenoid Control Circuit

Engine Controls Components
Cell 20: MAF Sensor, EVAP Components and EGR Valve
OBD II Symbol Description Notice
ESD Notice

Circuit Description

The PCM contains chips called Output Driver Modules that provide 7 switchable ground outputs for operating solenoids, relays, telltales, and other devices. Each of these ground outputs has fault lines that feed back to the PCM's microprocessor. When the output is OFF, the output driver should receive the 12 volts fed to the solenoid, relay, etc. When the output is ON, it should receive 0 volt since it is grounding the output. If it receives 0 volt when the output is OFF or 12 volts when the output is ON, it sets the fault line low. DTC P1646 is used to monitor the fault line of the EVAP Vent Valve.

Conditions for Running the DTC

•	DTC P1640 not set.

•	Engine running at least 10 seconds.

Conditions for Setting the DTC

Fault line is low for 2 seconds.

Action Taken When the DTC Sets

•	The PCM will illuminate the malfunction indicator lamp (MIL) when the diagnostic runs and fails.

•	The PCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records.

Conditions for Clearing the MIL/DTC

•	The PCM will turn the MIL OFF after three consecutive drive trips that the diagnostic runs and does not fail.

•	A Last Test Failed (current) DTC will clear when the diagnostic runs and does not fail.

•	A History DTC will clear after forty consecutive warm-up cycles with no failures of any emission related diagnostic test.

•	Use a scan tool to clear DTCs.

•	Interrupting PCM battery voltage may or may not clear DTCs. This practice is not recommended. Refer to Clearing Diagnostic Trouble Codes in PCM Description and Operation.

Diagnostic Aids

Use the Failure Rec. to aid in diagnosing an intermittent fault. Use the data captured when the DTC set to determine if an open or shorted condition caused the DTC to set.

Step

Action

Value(s)

Yes

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

Connect a scan tool.
Turn the key ON.

Are DTCs P1633 or P1634 also set?

Go to diagnosis for the DTC that is set

Go to Step 3

Using a scan tool view the EVAP Vent Valve Driver display.

Does the display indicate OK?

Go to Step 4

Go to Step 5

In Output Tests select EVAP Vent Valve.
Command the EVAP Vent Valve open for at least two seconds.
Check the EVAP Vent Valve Driver display.

Does the display indicate OK while the EVAP Vent Valve is commanded ON?

Go to Diagnostic Aids

Go to Step 8

Record the fluid life indexes, turn the key to LOCK and wait 30 seconds.
Disconnect PCM connector C2.
Turn the key ON.
Using DMM J 39200 measure the voltage to ground at PCM connector C2 terminal 29.

Is the voltage the same or more than the value specified?

10.0 volts

Go to Step 13

Go to Step 6

Disconnect the EVAP Vent Valve connector.
Measure the voltage to ground at EVAP Vent Valve connector terminal A (harness side).

Is the voltage the same or more than the value specified?

10.0 volts

Go to Step 7

Go to Step 12

Jumper the EVAP Vent Valve connector terminal A to terminal B.
Measure the voltage to ground at PCM connector C2 terminal 29.

Is the voltage the same or more than the value specified?

10.0 volts

Go to Step 9

Go to Step 10

Turn the key to LOCK.
Disconnect the EVAP Vent Valve connector.
Turn the key ON.
Using DMM J 39200 measure the voltage to ground at EVAP Vent Valve connector terminal B.

Is the voltage the same or more than the value specified?

0.5 volts

Go to Step 11

Go to Step 13

Replace the EVAP Vent Valve. Refer to Evaporative Emission Vent Valve Replacement .

Is the repair complete?

Go to Powertrain Control Module Diagnosis

Repair open or short to ground in the EVAP Vent Valve input circuit between the EVAP Vent Valve and the PCM.

Is the repair complete?

Go to Powertrain Control Module Diagnosis

Repair short to voltage in the EVAP Vent Valve input circuit between the EVAP Vent Valve and the PCM.

Is the repair complete?

Go to Powertrain Control Module Diagnosis

Check for and repair the following:

•	An open in the EVAP Vent Valve power feed circuit.

•	A short to ground (blown fuse) in the EVAP Vent Valve power feed circuit.

•	A shorted EVAP Vent Valve (blown fuse).

Is the repair complete?

Go to Powertrain Control Module Diagnosis

Check terminal contact at the PCM connector C2 terminal 29.
Repair terminal contact if needed.

Was terminal contact repaired?

Go to Powertrain Control Module Diagnosis

Go to Step 14

Replace the PCM. Refer to Powertrain Control Module Replacement/Programming .

Is the replacement complete?

Go to Powertrain Control Module Diagnosis