OBD-II trouble code
P0592: Cruise Control Multi-Function Input "B" Circuit Low
The "B" input has been pulled down below every recognised command band. On a pull-up circuit that means current is escaping to ground somewhere it should not — a short, not an open — and there is a single unplug-and-look test that settles where.
Quick facts
- System
- Powertrain
- Category
- Cruise Control
- Severity
- Low severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $0 – $400
- DIY difficulty
- Intermediate DIY
What does P0592 mean?
P0592 is a short-to-ground code, and reading it that way immediately cuts the possible causes roughly in half.
A multiplexed switch input is built as a voltage divider. The module supplies a reference through an internal pull-up resistor, the switch ladder provides a known resistance to ground, and the voltage at the junction is what gets measured. Every legal command corresponds to some resistance in that ladder, and the lowest-resistance command still leaves a defined amount of voltage on the wire. Below that value there is nothing for the module to recognise, so a reading under the bottom band means the circuit is being pulled harder toward ground than any button can pull it. Something is providing a resistance path lower than the ladder itself.
That is a physically different event from an open circuit, and it fails in the opposite direction from P0593. It is worth holding onto, because the two codes attract the same guesses and only one of them is ever caused by a broken wire.
The things that pull a signal wire down are conductive and they are usually wet or sharp. Water is the most common: a spill that reaches a switch pad, a leaking windscreen seal that drips onto a column connector, or condensation in a poorly sealed steering wheel assembly bridges adjacent pins with a resistance low enough to swamp the ladder. Abrasion is next. The harness leaving the column runs past a moving steering shaft and through a bulkhead, and insulation worn through at either point puts bare copper against grounded metal. Crushed wiring at the wheel hub, where the loom was pinched during reassembly, does the same thing in one spot. Inside the switch itself, a resistor that has failed short — rather than open, which is more common but produces a high reading — hands the module a near-zero path with no external damage to find.
The decisive test on this code is short and does not exist for its high-side twin. Unplug the switch assembly and read the circuit again. With the switch removed, the ladder's path to ground is gone entirely, so a healthy wire must float up to the pull-up's reference. If it does, the harness is intact and the short is inside the switch. If it stays low with nothing connected, the switch is innocent and the fault is somewhere between the connector and the module. One measurement, two possibilities eliminated, and no disassembly beyond a single plug.
One behavioural note that helps set expectations. Because a hard short sits below every band, the module usually cannot distinguish it from the lowest-resistance command, so on many vehicles cruise is disabled outright rather than behaving erratically. A complaint of a cruise system that simply does nothing, with this code stored, is consistent and does not indicate a second fault.
Common causes
- Signal wire chafed through against the steering column or a bulkhead grommet, shorting to ground
- Water or a spilled drink bridging pins inside the steering wheel switch assembly
- Condensation or a leaking seal wetting a connector behind the wheel or at the column
- Harness pinched or crushed at the wheel hub during airbag or clockspring reassembly
- Resistor inside the switch ladder failed short rather than open
- Contact dome collapsed and permanently bridging the lowest-resistance position
- Two conductors shorted together where one of them is a ground or a low-side circuit
- Corrosion inside a connector body creating a conductive path between adjacent terminals
- Damaged clockspring ribbon shorting a signal trace to the ground trace beside it
Symptoms
- Check engine light on with P0592 stored
- Cruise control disabled and refusing to arm at all
- Live data showing the "B" circuit sitting near zero volts with nothing pressed
- Fault appearing after rain, a car wash, or a spilled drink in the cabin
- Fault appearing shortly after steering wheel, airbag or clockspring work
- Other steering wheel controls on the same connector also inoperative
- Symptoms that come and go as the steering wheel is turned, if the short is intermittent
- Code returning immediately after being cleared, since a hard short is always present
Diagnostic steps
- 1.Read the live "B" circuit value with the key on and no button pressed. A reading near zero volts at rest confirms the circuit is being held down rather than opened.
- 2.Unplug the switch assembly and read the circuit again. This is the decisive test: a wire that rises to reference voltage with the switch removed is healthy, and the short is inside the switch.
- 3.If the circuit stays low with the switch disconnected, measure resistance from that wire to chassis ground. A low reading with nothing connected confirms a shorted harness.
- 4.Ask about recent water exposure. A spill, a car wash, a leaking windscreen seal or a blocked cowl drain are the most common ways this circuit ends up grounded.
- 5.Inspect the loom where it leaves the column and passes the bulkhead. Those are the two points where insulation wears through against a moving or sharp surface.
- 6.Check whether the harness was pinched at the wheel hub during recent service. A crushed conductor produces a permanent short in a location nothing else explains.
- 7.Open the switch connector and look for green corrosion or moisture tracks bridging adjacent terminals rather than assuming the wiring is at fault.
- 8.Wiggle the loom and turn the wheel lock to lock while watching live data if the fault is intermittent, then isolate the section where the reading drops.
- 9.Before working behind the steering wheel, follow the manufacturer's procedure for disabling the supplemental restraint system and observe the specified waiting period.
Repair cost
$0 – $400
Drying and cleaning a wet connector is often a labour-only repair of 0.5-1 hour. Repairing a chafed or crushed conductor is typically $80-$300 depending on where the damage sits and how much trim has to come out to reach it. A steering wheel control switch assembly with an internally shorted ladder is $30-$200 in parts plus 0.5-1.5 hours. Where the short is in the clockspring ribbon the part is $60-$350 with 1-2 hours of labour. The unplug-the-switch test costs a few minutes and decides which of these you are buying, so it is worth insisting it happens before any part is ordered.
Estimate your repair
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Open the Repair Cost Estimator with wiring harness / circuit repair preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.