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STS 116,000 miles . SES light comes on, with PCM P1633 code ' zero position ignition '. Light goes out when this code is cleared.

Ignition switch was replaced 4 years ago . Battery is 7 years old , but output seems fine and car starts and runs O.K. Just curious - other than clearing the code every few days - anybody have any thoughts about how to approach this ?

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Are you sure that is the code? Service manual shows that will not light up the SES.

DTC P1633

Circuit Description

The powertrain control module (PCM) receives three ignition inputs from the ignition switch: ignition 0 signal, ignition 1 signal, and crank signal. The PCM receives the ignition 0 signal with the ignition switch in the CRANK position. The ignition switch sends this signal through the Off/Run/Crank voltage circuit. The PCM uses a Class II ignition mode message and voltage input from separate systems to test the Off/Run/Crank voltage circuit. If the PCM detects an improper ignition 0 signal, DTC P1633 will set.

Conditions for Running the DTC

No Class II serial data circuit problem.

Conditions for Setting the DTC

The PCM detects an improper IGN 0 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 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.

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I thought P1633 was the only current code present when I cleared PCM codes previously - when the SES light went away . I just noticed P0125 code which was occasionally in history is now current.

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