P1586 – Throttle Control Unit Throttle Position Malfunction (Citroen / Peugeot)

By Reinier (Contact Me)
Last Updated 2022-03-28
Automobile Repair Shop Owner

Manufacturer Specific Definitions for P1586

Table of Contents

1. What Does Code P1586 Mean?
2. Where is the P1586 sensor located?
3. What are the common causes of code P1586?
4. What are the symptoms of code P1586?
5. Get Help with P1586

What Does Code P1586 Mean?

OBD II fault code P1586 is a manufacturer-specific trouble code that is defined by carmakers Citroen, Peugeot, Ford, Jaguar, Lincoln, Mercury, and Oldsmobile as, “Throttle Control Unit Throttle Position Malfunction”, and is set on these applications when the PCM (Powertrain Control Module) detects a malfunction in the throttle position sensor or the sensor’s control/signal circuits.

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. As a practical matter, 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 PCM as “closed” and b), this position serves as the reference point against which all throttle openings are measured in degrees of rotation of the throttle blade.

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 PCM.

During normal operation of the engine, the PCM monitors the position of the throttle blade continuously and also compares its actual position with the position the PCM expects to see. In addition, the PCM 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 PCM 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 PCM can exert precise control over the throttle position throughout the engine’s operating range, which reduces both fuel consumption and harmful exhaust emissions.

So when a failure or malfunction occurs that either causes an actual gross miscorrelation between the positions of the throttle blade and the throttle pedal, or a failure or malfunction occurs that the PCM interprets as a gross miscorrelation, the PCM will recognize that it cannot control the throttle position effectively. When this happens, the PCM will set an appropriate throttle control-related fault code and illuminate a warning light, but note that in many instances of code P1586 on the applications listed above, the PCM will also initiate and maintain a fail-safe or limp mode as a safety precaution.

In most cases, the PCM 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 P1586 sensor located?

This image shows an example of a drive-by-wire throttle control unit (yellow arrow), while the green arrow indicates the part of the throttle body that contains both the stepper motor and the electronic circuitry that controls the stepper motor. In all designs, drive-by-wire throttle bodies are located in the same position as conventional throttle bodies, i.e., directly in front of the intake manifold.

It should be noted, however, that while drive-by-wire throttle bodies are sometimes repairable, even on a DIY basis, repairs typically offer only a temporary solution. Therefore, the wiser option is always to replace worn, damaged, or defective electronic throttle bodies with an OEM part, or at least, an OEM-equivalent part to ensure reliable operation of the part over the long term.

What are the common causes of code P1586?

The most common causes of code P1586 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
• Excessive build-up of carbon and other deposits that prevent or inhibit the free movement of the throttle blade
• A defective or worn pedal position sensor assembly
• Defective or worn throttle blade position sensor
• Excessive mechanical wear of any moving part(s) in either (or both) the throttle pedal position sensor assembly and the throttle body
• The use of substandard or unsuitable electronic throttle bodies; while many drive-by-wire throttle bodies appear to be identical in all respects, the calibration of these parts are almost always application-specific, which means that drive-by-wire throttle bodies 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 P1586?

Common symptoms of code P1586 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 P1586
• 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

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