|Code||Fault Location||Probable Cause|
|P1542|| P1542 – Pedal Position Sensor Electrical (BMW, MINI) |
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Manufacturer Specific Definitions for P1542
|Audi||Throttle motor position sensor 1 - range/performance problem|
|Bmw||VVT CAN timeout, bank 1|
|Buick||A/C System High Pressure High Temperature|
|Cadillac||A/C System High Pressure High Temperature|
|Chevrolet||A/C System High Pressure High Temperature|
|Gm||A/C System, High Pressure/High Temperature Conditions|
|Honda||Passenger compartment heater standby signal circuit – high input|
|Mercedes-Benz||Accelerator pedal position (APP) sensor – signal|
|Mini||Pedal Position Sensor Electrical|
|Oldsmobile||A/C system -high pressure/high temperature|
|Volkswagen||Throttle motor position range/ performance problem|
What Does Code P1542 Mean?
OBD II fault code P1542 is a manufacturer-specific trouble code that is defined by carmakers BMW and MINI as, “Pedal Position Sensor Electrical”, and is set on these applications when the PCM (Powertrain Control Module) detects an abnormal electrical value in the throttle position sensor’s control and/or signal circuits.
NOTE: On BMW and MINI applications, the PCM (Powertrain Control Module) is known as the DME (Digital Motor Electronics).
On the vehicles listed above, there is no mechanical linkage such as a control cable between the throttle pedal and the throttle blade. Instead, these applications are fitted with so-called drive-by-wire throttle control systems that use electric motors to control the movement of the throttle blade.
In terms of operating principles, these systems use simple potentiometers on the throttle pedal that are linked to stepper motors in the throttle body. When the throttle pedal is in the rest position, no current passes to the throttle body, and in this state, the throttle plate is held open by a stopper, thus allowing enough air to enter the engine to let the engine start and run at idle. Note that a) this position is interpreted by the DME as “closed” and b), this position serves as the reference point against which all throttle openings are measured.
When the throttle pedal is depressed, the resistive element in the potentiometer causes progressively more current to pass to the throttle body. The changing current then activates the stepper motor in the throttle body to open the throttle blade to a position that corresponds with the position of the throttle pedal. Thus, in a fully functional throttle control system, the throttle blade will be 50 percent open when the throttle pedal is at 50 percent of its travel, but to verify this, the throttle body contains a dedicated position sensor that relays the actual position of the throttle blade to the DME.
During normal operation of the engine, the DME monitors the position of the throttle blade continuously and also compares its actual position with the position the DME expects to see. In addition, the DME monitors the correlation between the position of the throttle pedal and the actual position of the throttle blade, as opposed to its desired position.
It should be noted though, that since both the throttle pedal assembly and the throttle body assembly contain many moving parts, the DME has some ability to compensate for fair wear and tear of mechanical parts that could cause miscorrelations between the actual positions of the throttle pedal and the throttle blade. However, this ability is limited, and as result, the maximum allowable amount of mechanical wear of components is strictly defined, and therefore, maximum allowable deviations from perfect correlations between a throttle blade and a throttle pedal position are typically limited to less than 2 percent.
When pressure is removed from the throttle pedal, the control process reverses, in the sense that a diminishing current causes the throttle control system to close the throttle blade in direct proportion to the amount by which the throttle pedal is moving towards its rest position. Thus, if the throttle control system works equally well in both directions, the DME can exert precise control over the throttle position throughout the engine’s operating range, which reduces both fuel consumption and harmful exhaust emissions.
For this system to work as designed, however, the input signals from the pedal position sensor have to be valid, accurate, and plausible, and to ensure the integrity of all signals entering and leaving the throttle pedal positions sensor, the DME monitors all implicated electrical circuits continuously. These checks include looking for and recording spikes and dips and both voltage and current, as well as intermittent or sporadic breaks in continuity.
When the DME detects abnormal electrical values or breaks in continuity that exceed maximum allowable thresholds, it will recognize that it cannot control the throttle effectively, and it will set an appropriate throttle control-related fault code and illuminate a warning light. Note that in many instances of code P1542 on the applications listed above, the DME will also initiate and maintain a fail-safe or limp mode as a safety precaution.
In most cases, the DME will severely limit the engine speed and lock an automatic transmission into second or third gear, but in all cases, the limp mode will persist until the fault is found and corrected, with corrective action including performing specified throttle control and idle speed relearning procedures.
Where is the P1542 sensor located?
This image shows the throttle pedal (blue arrow) on a BMW Z4 application, with the red arrow showing the mechanical linkage between the pedal and the actual pedal position sensor, which is built into the black plastic enclosure behind the pedal.
Note that while it is possible to replace the pedal position sensor on almost all BMW and MINI models on a DIY basis, the replacement sensor has to be integrated into the larger throttle control system in all cases. Note, though, that while this is (sometimes) also possible to do on a DIY basis, the procedure can typically only be performed with dealer-grade diagnostic equipment and up-to-date software. Therefore, the better option is to seek professional assistance with diagnosing, replacing, and/or programming of any suspect component(s) in throttle control systems on BMW and MINI applications.
What are the common causes of code P1542?
The most common causes of code P1542 on listed applications are largely similar across all applications, and could include one or more of the following-
- Damaged, burnt, shorted, disconnected, or corroded wiring and/or connectors anywhere in the throttle control system
- A defective or worn pedal position sensor assembly
- Excessive mechanical wear of any moving part(s) in the throttle pedal position sensor assembly
- The use of substandard or unsuitable electronic throttle pedal position sensors; while many drive-by-wire throttle pedal sensors may appear to be identical in all respects, the calibration of these parts are almost always application-specific, which means that drive-by-wire throttle pedal sensors are typically not interchangeable- even if they fit on multiple applications
- Disconnecting the battery without installing a memory saving device; doing this could cause one or more control modules to lose programming, which could include learned values for the throttle control system
- Damaged or corrupted software in the PCM
- Failed or failing PCM, but note that since this is a rare event, the fault must be sought elsewhere before any control module is replaced or reprogrammed
What are the symptoms of code P1542?
Common symptoms of code P1542 are similar across all listed applications, and could include one or more of the following-
- Stored trouble code and an illuminated warning light
- Depending on the application and the nature of the problem, multiple additional codes may be present along with P1542, and particularly codes that relate to pedal position sensor and throttle blade correlation issues
- The cruise control system will be deactivated or unavailable
- Throttle responses may be poor and/or unpredictable, even if the vehicle is not in a limp mode
- The engine may be hard to start
- The engine may stumble or hesitate upon acceleration
- The idling quality may be poor, or the engine may not idle at all
- The engine may stall repeatedly and/or unexpectedly
- Gearshifts may be harsh or unpredictable
- Fuel consumption may increase
- The vehicle may be locked into a limp mode that will typically persist until the fault is corrected