Tech Tips: Full Throttle

It Works Just Like a Carburetor. Here’s How You Fix It.
There was a time not long ago when fuel was delivered to the engine through a carburetor. This device had a throttle plate, connected to the accelerator pedal via a cable, that would allow an increasing amount of air/fuel mixture into the engine as the pedal was pressed. So, as the driver pressed down on the accelerator, the car would go faster. Well, the carburetor is long gone, but the need to control the amount of air rushing into the engine remains.

Enter the throttle body. It works, essentially, the same as the carburetor. As electronic capabilities increased, the idea of removing the cable between the pedal and throttle became a reality. And today, this reality can be seen in the throttle body found in the 2.4L 4-cylinder engine and the 3.6L V6.

When a component is controlled electronically instead of mechanically, the term to describe that control is drive-by-wire. That’s because the signals that control the operation are sent electrically, via a wire. Airplanes use drive-by-wire technology extensively throughout the aircraft. But, its application on automobiles is relatively new in comparison.

With a drive-by-wire throttle body, the signal that operates this device is generated by the accelerator pedal. A sensor detects the position of the accelerator. That signal is sent to the PCM that, in turn, sends a signal to the throttle body to open to a specified position. The electronic signal replaces the cable.

The electronic throttle control (ETC) motor is controlled using an H-bridge circuit inside the PCM. This circuit enables a voltage (from the accelerator pedal signal) to be applied across a load in either direction. This arrangement is used to reverse the polarity/direction of the ETC motor to open and close the throttle blade.

Experimental work is also being done with drive-by-wire steering, which, in theory, would eliminate the mechanical connection between the steering wheel and steering gear. We’ll have to wait and see how that develops in the years ahead.

The drive-by-wire design allows the engine designer to mount the throttle body in a more suitable location. Traditionally, the throttle body is on top of the engine. On the 2.4L World Engine, the throttle body is mounted on the front side of the engine just above the oil pan. This is where you might normally find an alternator or power steering pump.

The throttle body for this engine is shown in Figure 1. Note that the inlet and throttle blade look like a conventional throttle component, but there is no connection point for the cable. Instead, there is an electrical connector into which the cable is plugged. In addition, there is not a separate throttle body position sensor (TPS). It is enclosed within the housing, along with the ETC motor.

Due to the electronic design of this throttle body component, diagnosing problems is a little more difficult. Mainly because electrical problems are tougher to detect then mechanical ones. Fortunately, on-board diagnostics are here to help. The PCM performs ongoing diagnostics off the DC motor and the circuits. If the PCM detects variations in the current draw or pulse width modulation, a diagnostic trouble code (DTC) will be generated. Other performance issues can also be detected.

P0121, P0122 and P0123 are DTCs that indicate performance problems and circuit issues with the throttle body. And, if trouble code P2101 is retrieved, there is a problem with the performance of the ETC motor. Follow the diagnostic procedures outlined in the specific service manual for the vehicle being repaired. A typical vehicle with this 4-cylinder engine and the drive-by-wire throttle body is the 2012 Chrysler 200.

If a problem exists with the ETC motor or throttle position sensor, and replacement is indicated to solve the problem, the entire throttle body assembly must be replaced. These two components are located within the housing (refer to Figure 1) and not serviced separately. This is a major difference between this design and its mechanical counterpart. On the cable-driven unit, those components can be serviced separately.

As with conventional throttle body units, the inlet and throttle blade can become dirty. This can cause performance problems, but usually, this condition can be detected by a rough idle. With an electronic unit, two separate trouble codes can indicate this problem. P2111 indicates the throttle blade is unable to open, P2112 indicates the throttle blade is unable to close. Both problems are caused by a build-up of dirt and carbon. And, both problems can be solved by using the same product, Mopar® Throttle Body Cleaner, P/N 04897156AD.

Because the electronic throttle body is not very easy to reach, often this product can be sprayed down a vacuum line (such as brake booster vacuum line). It can be drawn into the inlet of the throttle body, cleaning it and the throttle blade. This should correct the opening and closing issues. In extreme cases, remove the throttle body from the vehicle and clean it by hand.

Under some circumstances, it might be necessary to remove the throttle body assembly. Sometimes it may be to thoroughly clean the inlet and throttle blade, but more often it will be to replace it. The procedure is pretty straightforward.

As always, safety comes first, so disconnect and isolate the negative battery cable. Next, remove the throttle body air intake hose. To obtain more room, you can also remove the air cleaner box. Disconnect the throttle body electrical connector cable (1) from the assembly (2) as shown in Figure 2. Remove the throttle body support bracket bolt (the bracket is on the RH side of the inlet), then remove the four retaining bolts. The throttle body assembly can then be removed from the engine compartment.

Before installing the new assembly, inspect the intake-manifold-to-throttle-body gasket for damage. If it is damaged, it must be replaced. If it is in good condition, it can be reused.

Install the new throttle body assembly by placing it against the intake manifold gasket. Install the support bracket, located on the RH side of the inlet, with the retaining bolt. Hand tighten the bolt. Next, install the four assembly retaining bolts and hand tighten.

The retaining bolts must be tightened in the required criss-cross pattern to the proper torques specification (65 in-lbs). Then, tighten the support bracket bolt to 18 ft-lbs. Do not over-torque the retaining bolts.

To finish the installation, connect the electrical connector cable, install the air intake hose (and the air cleaner box if it was removed) and reconnect the negative battery cable.

WARNING: DO NOT place fingers in or around the throttle body plate. If the throttle body is energized, the throttle plate could move causing personal injury. Always disconnect the negative battery cable prior to servicing the throttle body.

CAUTION: DO NOT move the throttle plate while power is connected to the throttle body. This may cause fault codes to set.