P2173 OBD-II Trouble Code: Throttle Actuator Control System - High Airflow Detected

Check Engine Light

P2173 code definition

Throttle Actuator Control System - High Airflow Detected

What the P2173 code means

Code P2173 means that there is a vacuum leak somewhere in the intake system or one or more of the sensors that monitors intake pressures has malfunctioned.

What causes the P2173 code?

The Powertrain Control Module (PCM) monitors the intake manifold pressures for calculating air fuel ratio. The most likely cause of this code will be a vacuum leak. The intake manifold is the primary culprit when a vacuum leaks occur, but there is many other systems tap into the intake manifolds vacuum supply. If any other systems should leak vacuum, a vacuum leak will occur. The list of components and systems are as follows:

  • Vacuum leak
  • Manifold Absolute Pressure (MAP) sensor
  • Mass Airflow (MAF) sensor
  • Exhaust Gas Recirculation (EGR) valve
  • Broken vacuum hoses connected to the intake manifold
  • Short to power or ground in the 5 volt reference circuit
  • Vacuum brake booster
  • PCM
  • Electronic Throttle Control System (ETCS) / Throttle Body

Note: The ETCS is actually more than one component:

  • Throttle Position Sensor (TPS)
  • Throttle Valve Actuator
  • Throttle Valve

What are the symptoms of the P2173 code?

This code is set when the PCM believes there is excessive air entering the engine. When this occurs, it creates a lean running condition, meaning there is too much air in comparison to fuel. When this condition exists, the motor will usually misfire. Most identify this as rough running. Other possible symptoms are as follows:

  • High idle
  • Poor fuel mileage
  • Check Engine Light
  • Hesitation
  • Lack of power
  • Overheating
  • Hard start
  • Crank no start

How does a mechanic diagnose the P2173 code?

The primary cause of this code is a vacuum leak. This is what this code is suppose to indicate. For this reason the technician should expect to find a vacuum leak. Locating a vacuum leak can be done in a variety of ways.

First step to any diagnosis is to observe. Often times a vacuum leak will make a loud whistle or whooshing sound. Simply following the sound to its source will confirm the problem. If there isn’t any obvious sound, than there are two other techniques commonly used.

Lightly spraying a mist of starter fluid, brake cleaner or carburetor cleaner in suspected areas will often reveals a vacuum leak. When one of these sprays enters into the intake manifold via a vacuum leak or throttle valve, the motor will react with a change in RPM (revolutions per minute). Spray these chemicals liberally at a suspected and localized area. If a mist were to engulf the entire engine compartment and there is a change in RPM, then there is no way to know where the mist entered the motor. For this reason lightly spraying at suspected areas is necessary to isolate, where there is a possible intake leak.

Another technique that often reveals the source of air leaking into a motor is with the use of a smoke machine. This should be used with the motor off and connected to a vacuum port. This machine creates smoke under pressure that it injects into the intake manifold and all the vacuum lines connected to it. As the pressure builds in the intake system, smoke will be forced out of any vacuum leak in the entire system. A smoke machine is often used to diagnose EVAP systems as well.

If there is no sign of a vacuum leak, the next thing the technician should suspect is a problem with the system that the PCM uses to monitor intake manifold pressures. The PCM uses the induction (Induction is the process of sucking air into a motor for combustion) monitoring system to adjust air fuel ratio depending on the conditions in the intake manifold. It is this system that will detect excessive air flow into the motor. This system consists of the MAP or MAF sensor, TPS, EGR valve, PCM, O2 sensor, intake manifold and any system that uses vacuum to operate.

Often times this system simply misinterprets the information it receives from these sensors and sets the wrong code. A malfunction in any of these sensors will usually set the appropriate code for their malfunction, but this is not always the case. Knowing the difference depends on the experience of different technicians.

Common mistakes when diagnosing the P2173 code

A thorough check for vacuum leaks is often harder said than done. If a technician fails to find the leak, he or she may suspect a sensor problem and spend a lot of time testing each suspected sensor one at a time, only to find that they are all good. The next process will be to again look harder for a vacuum leak. Vacuum leaks can occur in unexpected places sometimes making them challenging to identify.

After a thorough inspection of the vacuum system and it is determined there isn’t a vacuum leak, the technician should look closer at the scan tool data. This data isn’t always simple to interpret. All sensors use a 5 volt reference instead of the unsteady 13 to 15.5 volts that exist when a vehicle is running. The 5 volt reference is in place to give the PCM a constant, and steady reference point for any changes that occur in all sensors. If this 5 volt reference is compromised by a short to ground or power, the results are unpredictable.

Often times disconnecting each sensor one at a time and monitoring the reference voltage with a multimeter is necessary to pinpoint a problem. The programming in each vehicle will differ year to year and manufacturer to manufacturer. For this reason, the results of a sensor failure or reference voltage corruption is often one of the most challenging system to diagnose.

How serious is the P2173 code?

This code is moderately serious only because it is likely to accompany drivability symptoms. In the case of a very large vacuum leak, which is likely to make the car un-drivable, burnt valves in the head is possible. Most drivers will call a tow truck at this point, but for those who choose to continue driving, more problems can be created.

In most cases there will be annoying drivability symptoms that motivates the owner to seek a mechanic. It is possible on some vehicles to only exhibit mild symptoms and a Check Engine Light, but different codes are usually set.

What repairs can fix the P2173 code?

Most likely a vacuum leak will need to be repaired. Vacuum leaks can occur from many sources.

Additional comments for consideration regarding the P2173 code

This code is only used by Chrysler vehicles and on a few years model of Hyundai’s. This includes Jeep and Dodge vehicles. In addition to its little use, Chrysler assigns two different code definitions to this code. The official OBD-II (On Board Diagnostics, Version II) code definition is the one stated at the beginning of this article. The alternate definition used by Chrysler products is “High Airflow/Vacuum Leak Detected (Slow Accumulation).” Either way, the code indicates there is a vacuum leak. The alternate Chrysler code repair procedure directs the technician to the EGR valve first.

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