P0592 OBD-II Trouble Code: Cruise Control Multi-Function Input "B" Circuit Low

What the P0592 code means

A P0592 code means that the powertrain control module (PCM) has detected a fault (electrical malfunction) in the cruise control input circuit.

What causes a P0592 code?

In many cases, the P0592 code is caused by a failed cruise control switch. Since the switch is in the vehicle’s interior, it’s not unusual for it to have liquids spilled on it, creating an open or shorted condition.

What are the symptoms of a P592 code?

In most cases, the cruise control system (CCS) won’t work, as the PCM has run self-tests on it and locked out the function. Other symptoms can include an illuminated malfunction indicator lamp (MIL) or possibly limp-in mode.

How does a mechanic diagnose a P0592 code?

Trouble codes are registered when the PCM detects readings from sensors or systems that are outside of norms. In the case of the CCS switch, the PCM is set to see a neutral position when the key is turned on. If it detects anything else, such as no signal or two positions at once, the PCM will read that as an open or short circuit.

A technician will need a digital multimeter (DMM) and model-specific wiring diagram.

• Check fuses, wiring harnesses and switch terminals. Look for chafing, pinched wires, corrosion or any other obvious damage. Check for bent, broken or backed-out pins on connectors. Repair/replace as needed.

• Use the DMM to perform resistance and continuity checks. Different CCS systems will use different switch designs, so refer to the wiring diagram and repair manual to determine your vehicle’s switch design and how to perform a check.

• If continuity and resistance are correct, it could be a PCM fault or intermittent circuit problem.

• If continuity and resistance are outside of norms, suspect the CCS switch or spiral cable.

• The cruise control servo which controls throttle settings is dependent on engine vacuum, and uses a signal from the driver to adjust vehicle speed. Check vacuum supply hoses, replace any hoses that are questionable or disconnected.

• If vacuum lines appear normal, perform vacuum pressure test and compare to manufacturer’s specs.

• Most systems include a one-way valve, which is easily tested by attempting to blow air through it in both directions. Air should only pass through in one direction. Replace one-way vacuum valve if needed.

• If vacuum lines and switch continuity/resistance all check OK, suspect the spiral cable. Before checking circuits in the spiral cable, ensure the battery is disconnected, ignition off and all connectors disconnected.

• If switch continuity or resistance are incorrect, replace the switch.

Common mistakes while diagnosing P0592 code

After replacing any faulty components, be sure to check for blown fuses. Sometimes multiple components are unnecessarily replaced simply because of a blown fuse.

How serious is a P0592 code?

While a vehicle with a P0592 code may still run and drive, it will most likely not have a working cruise control system.

What repairs can fix a P0592 code?

Replacement of cruise control switch or wiring, or repair of vacuum lines to servo at throttle.

Additional comments for consideration for P0592 code

Since the cruise control switch is often located on the steering wheel, it may be necessary to remove the driver’s airbag to access the switch. This can be a dangerous procedure – if you do not have the training and tools, it’s best to leave this to a professional. The airbag’s circuit passes through the spiral cable – do not attempt to circuit-check the spiral cable unless the ignition is off, battery disconnected and all connectors disconnected.

In vehicles that have a multi-function switch at the turn signal stalk, multiple failures may present themselves, including cruise, headlight dimmer, audio controls, wipers, etc. In these instances, the clock spring is often at fault. Do not attempt disassembly of the clock spring unless you are prepared to replace it, as a clock spring is near impossible to repair or reassemble.

Need help with a P0592 code?

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