DTC P1634 Ignition 1 Switch Circuit. Cadillac DeVille 2000

For 1990-2009 cars only

Makes 🢒 Cadillac 🢒 2000 🢒 DeVille 🢒 DTC 🢒 DTC P1634 Ignition 1 Switch Circuit

Refer to

PCM Power and Ground

Engine Controls Components
Powertrain Control Module (PCM)
DLC and MIL
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
Ignition Switch
Rear Fuse Block Battery Voltage
RR BLO, RRDR MDL, HVAC BLO, STOP LP, IGN SW, and TSIG/HAZ Fuses
RR BLO, RRDR MDL, HVAC BLO, STOP LP, IGN SW, and TSIG/HAZ Fuses
Power and Grounding Connector End Views Fuse Blocks and Ignition Switch
Ignition Switch
Starting and Charging Schematics
Underhood Fuse Block Battery Voltage
START Circuit Breaker, PCM IGN and IGN1 Fuses
Power and Grounding Connector End Views Fuse Blocks and Ignition Switch
Powertrain Control Module Connector End Views
G100
in Engine Controls Schematics.

The PCM receives three ignition inputs from the ignition switch: IGN 0, IGN 1, and CRANK Request. The PCM receives the IGN 1 input with the ignition switch in RUN and START. The PCM uses a class 2 ignition mode message, and the voltage input from two separate systems to test the IGN 1 circuit. If the PCM detects an improper IGN 1 input, DTC P1634 will set.

Conditions for Running the DTC

No Class 2 serial data circuit problem.

Conditions for Setting the DTC

The PCM detects an improper IGN 1 input.

Action Taken When the DTC Sets

•	The PCM will not illuminate the malfunction indicator lamp (MIL).

•	The PCM will store conditions which were present when the DTC set as Fail Records information only.

Conditions for Clearing the DTC

•	The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.

•	The DTC can be cleared by using the scan tool Clear DTC Information function.

Diagnostic Aids

If this DTC is intermittent check terminal contact at the PCM and the condition of the CKT 639 splice for an intermittent open condition.

Step	Action	Values	Yes	No
1	Was the Powertrain On-Board Diagnostic (OBD) System Check performed?	--	Go to Step 2	Go to Powertrain On Board Diagnostic (OBD) System Check
2	Observe the 12 Volt Reference display on the scan tool. Does the 12 Volt Reference display indicate FAULT?	--	Go to Step 3	Refer to Diagnostic Aids
3	Turn OFF the ignition switch. Disconnect the PCM connector. Turn the ignition switch to the RUN, and START positions. Using the J 39200 DMM, measure the voltage between the IGN 1 circuit and ground. Does the DMM display a voltage near the specified value for each ignition switch position?	B+	Go to Step 7	Go to Step 4
4	Does the DMM display a voltage near the specified value for any ignition switch position?	B+	Go to Step 8	Go to Step 5
5	Test for an open IGN 1 circuit. If a problem is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems. Was a problem found?	--	Go to Step 10	Go to Step 6
6	Inspect for poor connections at the ignition switch. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. If a problem is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems. Was a problem found?	--	Go to Step 10	Go to Step 8
7	Inspect for poor connections at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. If a problem is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems. Was a problem found?	--	Go to Step 10	Go to Step 9
8	Replace the ignition switch. Refer to Ignition Lock Cylinder Replacement - On Vehicle in Steering Wheel and Column - Tilt. Is action complete?	--	Go to Step 10	--
9	Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is action complete?	--	Go to Step 10	--
10	Review and record the scan tool Fail Record data. Clear the DTCs. Turn ON the ignition switch with the engine OFF. Using the scan tool, observe the Specific DTC Information for DTC P1634 until the test runs. Does the scan tool indicate that DTC P1634 passed?	--	System OK	Go to Step 2