Technical Description of OBD-II Trouble Code
The circuit for Transmission Mode Switch B is experiencing low voltage.
What does that mean?
This is a generic diagnostic trouble code (DTC) that applies to OBD-II vehicles, including those from GMC, Chevrolet, Ford, Buick, Dodge, and others. The specific repair steps may vary depending on the year, make, model, and powertrain configuration of the vehicle.
The Transmission Control Module (TCM) monitors all the sensors and switches involved in the operation of the transmission. Modern automatic transmissions have various features, such as cruise control, that are controlled by the TCM. In this article, we will focus on the tow/haul mode switch, which allows the operator to adjust the transmission ratios and shift patterns for towing or carrying heavy loads. The proper functioning of this switch is crucial for the tow/haul function and other related systems. However, the specific design and operation of this switch can vary significantly between manufacturers, so it is important to identify the correct mode switch for your vehicle.
The letter “B” in this code can have different meanings or distinguishing factors depending on the specific case. It is essential to consult the appropriate service information before attempting any troubleshooting steps to ensure accurate diagnosis of uncommon or obscure faults. This article provides general information and serves as a learning tool.
The Engine Control Module (ECM) will activate the Malfunction Indicator Lamp (MIL) and display the P071E code, along with related codes (P071D, P071F), when it detects a malfunction in the mode switch. In most cases, tow/haul switches are located on or near the shift lever, either as a button on the end of the lever or on the dashboard. The location can vary significantly between vehicles, so consult the service manual for precise information.
The P071E code is triggered when the ECM and/or TCM detects a low electrical condition in the “B” transmission mode switch circuit.
Here is an example of a stalk-mounted transmission tow/haul mode switch:
What is the severity of this DTC?
The severity of this DTC depends on the specific mode switch associated with the vehicle’s fault. In the case of the tow/haul switch, the severity is considered low. However, it is advisable to avoid heavy loads and towing to prevent unnecessary stress on the transmission and its components.
What are some of the symptoms of the code?
Symptoms of a P071E trouble code may include:
What are some of the common causes of the code?
The causes of the P071E code may include:
What are some P071E troubleshooting steps?
Basic Step #1
The starting point for troubleshooting may vary depending on the available tools and references. If your scanner has monitoring capabilities (DATA STREAM), you can use it to monitor the values and operation of the mode switch. Toggle the switch on and off to see if the scanner recognizes the inputs. Keep in mind that there may be a slight delay, so allow a few seconds when monitoring switches.
If the mode switch appears inoperative according to the scanner, you can try jumping some pins at the switch’s connector to test the circuit. If the circuit is ruled out and the switch is still not functioning, proceed to test the switch itself. These are general guidelines, and it is recommended to consult the service manual for specific specifications and procedures.
Basic Step #2
If possible, test the mode switch itself. In most cases, these switches are simple on/off sensors that signal the appropriate module(s) (e.g., TCM, BCM, ECM) about your towing/load requirements, enabling modified shift patterns. A continuity test with an ohm meter can determine the functionality of the sensor. Keep in mind that some sensors may be integrated into the shift lever, so research the correct connectors/pins to monitor with a multimeter.
NOTE: Always ensure that the transmission fluid levels and quality are adequate and well-maintained when dealing with any transmission fault.
