Check Continuity on Gmc 4wd Switch

P2771 code definition

Exhibited on all-wheel or four-wheel-drive vehicles only, a P2771 trouble code signifies a fault with the four-wheel-drive low switch circuit. Subsequently, the Powertrain Control Module (PCM) stores the trouble code and illuminates the Check Engine light. Associated codes include P2772, P2773, and P2774.

What the P2771 code means

The four-wheel-drive switch actuates the changing of gears ratios in the four-wheel-drive system. When PCM detects an abnormal reading in the transfer case control system, which contains the four-wheel-drive low switch circuit, a P2771 trouble code is sent to the PCM and the Check Engine light illuminates.

What causes the P2771 code?

The causes of a P2771 trouble code ranges from faulty solenoids, sensors, and switches to defective wiring and connectors. A malfunctioning four-wheel-drive switch or actuator can also cause the storage of this code.

What are the symptoms of the P2771 code?

While the storing of a P2771 trouble code might not cause any outward symptoms, it could also result in a total failure by the transfer case. In addition to the illumination of the Check Engine Light, this code can be exhibited through such common symptoms as a failure to shift from two-wheel to four-wheel-drive, engine stalling when stopped, and difficulty in shifting.

How does a mechanic diagnose the P2771 code?

To properly diagnose a P2771 trouble code, the mechanic should have an advanced scanner and a digital volt/ohmmeter. The mechanic should also perform the following steps:

• Start by checking out all wiring, connectors, and components.

• Download any stored codes and freeze frame data for later use if needed. The mechanic can do this by connecting the code reader to the diagnostic connector.

• If, after clearing the code, it immediately returns, check the battery voltage on the input side of the switch to see what the voltage reading is. Use a manufacturer's wiring schematic to find the four-wheel-drive switch.

• In cases of no voltage, make sure to disconnect any related control modules and check the continuity between the fuse and the input circuit at the clutch position sensor using a digital volt/ohmmeter.

• If you detect voltage, use the scanner to turn the four-wheel-drive system on, checking for voltage on the output size of the switch. If no voltage is present on the output side of the switch, then the four-wheel-drive switch is most likely at fault.

• If needed, check circuit continuity and resistance between the switch and the PCM. The mechanic should make sure to disconnect any related control modules to prevent memory loss.

• Clear the code and test the system to make sure of success and to see if the code returns.

Common mistakes when diagnosing the P2771 code

Mechanics replace or rebuild transfer cases when not needed when a P2771 trouble code is stored in the erroneous assumption this might fix the problem and clear the code. This fix for a P2771 trouble code is extraneous and expensive for vehicle owners.

How serious is the P2771 code?

When suffering from a P2771 trouble code, a vehicle transfer case can suffer a total failure. The vehicle can also have other problems, including shifting from two-wheel to four-wheel-drive and the engine stalling while the vehicle is stopped.

What repairs can fix the P2771 code?

After inspecting and diagnosing a P2771 trouble code, mechanics should make the following repairs as needed:

• Replace any damaged wiring, connectors, or other components.

• Replace the four-wheel-drive switch if its proves to be faulty upon testing with the digital volt/ohmmeter.

• Replace any additional open or shorted circuits and connectors after additional testing.

• Replace and reprogram the PCM if it is found to be at fault.

If a P2771 trouble code is stored in a two-wheel-drive vehicle, the mechanic should check the PCM as the problem most likely lies there. In a case such as this, the PCM itself is at fault or is suffering from a programming error.

Need help with a P2771 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

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Source: https://www.yourmechanic.com/article/p2771-obd-ii-trouble-code-4wd-low-switch-circuit-by-cheryl-knight

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