P071B Transmission Mode Switch A Circuit Low
Description and meaning of DTC p071b
This is a generic powertrain diagnostic trouble code (DTC) and typically applies to OBD-II vehicles. That may include but is not limited to vehicles from GMC, Chevrolet, Ford, Buick, Dodge, etc. Although generic, the exact repair steps may vary depending on year, make, model and powertrain configuration. The Transmission Control Module (TCM) monitors all the sensors and switches involved in the operation of the transmission. This day in age, automatic transmissions (a. k. a A/T) have more creature comforts than ever before. For instance, at times, cruise control is monitored and controlled by the TCM (among possible other modules). The example I will use in this article is, the tow/haul mode, it is enabled by the operator to modify the ratios and shift patterns to accommodate varying loads and/or towing demands. The operation of this switch is imperative to the functionality of the tow/haul function among other possibly included systems. This will vary significantly between manufacturers so make sure to know WHICH mode switch applies to your current fault and specific make and model. The letter A in this code, in this case anyway, could have multiple different definitions/ distinguishing factors. Most times, these will vary, so make sure to acquire the appropriate service information before performing any invasive troubleshooting steps. This is not only important but required to accurately troubleshoot obscure or non-common faults. Use this as a learning tool, given the generality of the article. The ECM illuminates the MIL (Malfunction Indicator Lamp) with P071B and/or related codes (P071A, P071C) when it detects a malfunction in the mode switch. The majority of the time, when it comes to tow/haul switch, they are located on or near the shift lever. On a stalk-style shifter, it may be a button on the end of the lever. On console-style shifters, it may be on the dash. Another factor that varies significantly between vehicles, so refer to your service manual for location. The P071B Transmission Mode Switch A Circuit Low code gets activated when the ECM (Engine Control Module) and/or the TCM detects a low electrical condition in the A transmission mode switch circuit.
p071b diagnostic trouble code symptoms
Symptoms of a P071B trouble code may include:Mode switch inoperative (e. g. tow/haul mode switch, sport mode switch, etc. )Erratic and/or abnormal switch operationInefficient shift patternLow power under heavy load/towingNot downshifting when torque is needed
DTC p071b - possible causes
Causes for this P071B code may include:Defective or damaged mode switchCorrosion causing high resistance (e. g. connectors, pins, grounds, etc. )Wiring issue (e. g. frayed, open, short to power, short to ground, etc. )Defective shift leverTCM (Transmission Control Module) issueFuse/box issue
How to fix OBD-II diagnostic trouble code p071b
Basic Step #1Depending on what tools/references you have at your disposal, your start point may be different. That said, if your scanner has any monitoring capabilities (DATA STREAM), you may be able to monitor the values and/or operation of your particular mode switch. If so, toggle the switch on and off to see if your scanner recognizes your inputs. There may be a lag here so a few seconds delay is always a good idea when monitoring switches. Not only that, but if you find the mode switch inoperative according to your scanner, you may be able to jump some pins at the mode switch's connector to rule out the circuit. If the circuit is ruled out in this manner, and the switch is still inoperative, I would move on to testing the switch itself. Obviously these are general guidelines but with an moderately able scan tool, troubleshooting CAN be pain-free if you know what you're looking for. Refer to service manual for specs/procedures. Basic Step #2Test the switch itself, if possible. Most times, these switches are just to signal to the appropriate module(s) (e. g. TCM, BCM (Body Control Module), ECM, etc. ) your towing/load needs so it can implement modified shift patterns. That said, the majority of these I've run into are on/off style. This means, that a simple continuity test with an ohm meter can determine the functionality of the sensor. Now, these sensors are sometime incorporated into the shift lever so make sure to research which connectors/pins you need to monitor with your multimeter. NOTE: As with any transmission fault, always ensure fluid levels and quality are adequate and well maintained.