Cruise Control Multi-Function Input "A"/"B" Correlation
P0585 indicates the PCM has detected a mismatch between two input signals from the multifunction switch (typically the steering column stalk that controls cruise control, turn signals, and wipers). The two input channels are not correlating as expected, suggesting a wiring or switch component failure.
What You Might Notice
- Inoperative cruise control system
- Erratic speedometer or odometer readings
- Flashing or unresponsive cruise control indicator lamp
- Turn signal or wiper control issues
- Additional related diagnostic trouble codes stored
Most Common Causes
- 1
Defective multifunction switch
The steering column stalk switch that controls cruise control and other functions has failed internally, causing signal correlation loss between its dual input channels.
- 2
Wiring harness damage or corrosion
Corroded or damaged wires in the multifunction switch harness prevent proper signal transmission to the PCM, causing the A/B input mismatch.
- 3
PCM connector issues
Loose, corroded, or damaged connectors at the PCM prevent reliable signal reception from the multifunction switch inputs.
- 4
PCM software fault or internal failure
A defective PCM unable to properly process multifunction switch signals, though this is less common than switch or wiring failures.
How to Diagnose It
- 1
Check Defective multifunction switch — The steering column stalk switch that controls cruise control and other functions has failed internally, causing signal correlation loss between its dual input channels.
- 2
Check Wiring harness damage or corrosion — Corroded or damaged wires in the multifunction switch harness prevent proper signal transmission to the PCM, causing the A/B input mismatch.
- 3
Check PCM connector issues — Loose, corroded, or damaged connectors at the PCM prevent reliable signal reception from the multifunction switch inputs.
- 4
Check PCM software fault or internal failure — A defective PCM unable to properly process multifunction switch signals, though this is less common than switch or wiring failures.
How to Fix It
- 1
Replace multifunction switch
Remove the steering column upper shroud and replace the defective multifunction switch stalk. This is the most common repair for this code. Verify cruise control and other stalk functions operate properly after installation.
- 2
Inspect and repair wiring harness
Examine the multifunction switch wiring harness for corrosion, breaks, or loose connections. Clean corroded terminals with electrical contact cleaner or replace damaged wire sections as needed.
- 3
Check and reseat PCM connectors
Locate the PCM under the dashboard or engine bay and inspect all connectors for corrosion or loose pins. Disconnect, clean with electrical contact cleaner, and reconnect firmly. Clear the code and retest.
- 4
Replace PCM if switch and wiring are good
If the multifunction switch, wiring, and connectors test good but the code persists, the PCM may have failed internally and require replacement and reprogramming.
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