P0704 Malfunction of the clutch switch input circuit

OBD-II Trouble Code - P0704 - Data Sheet

P0704 - Clutch Switch Input Circuit Malfunction

What does trouble code P0704 mean?

This Diagnostic Trouble Code (DTC) is a generic transmission code, which means it applies to all vehicles since 1996 (Ford, Honda, Mazda, Mercedes, VW, etc.). Although general in nature, the specific repair steps may differ depending on the brand / model.

If a P0704 code was stored in your OBD-II vehicle, it simply means that the powertrain control module (PCM) has detected a malfunction in the clutch switch input circuit. This code only applies to vehicles equipped with a manual transmission.

The PCM controls certain functions of the manual transmission. The position of the gear selector and the position of the clutch pedal are among these functions. Some models also monitor the turbine input and output speed to determine the amount of clutch slip.

The clutch is the mechanical clutch that connects the engine to the transmission. In most cases, it is actuated by a rod (with a foot pedal at the end) that pushes the plunger of the hydraulic clutch master cylinder mounted on the firewall. When the clutch master cylinder is depressed, hydraulic fluid is forced into the slave cylinder (mounted on the transmission). The slave cylinder actuates the clutch pressure plate, allowing the engine to be engaged and disengaged from the transmission as needed. Some models use a cable-actuated clutch, but this type of system is becoming less common. Pressing the pedal with your left foot disengages the transmission from the engine. Releasing the pedal allows the clutch to engage the engine flywheel, moving the vehicle in the desired direction.

The primary function of the clutch switch is to act as a safety feature to prevent the engine from starting when the transmission is inadvertently engaged. The clutch switch is primarily intended to interrupt the starter signal (from the ignition switch) so that the starter will not be activated until the clutch pedal is depressed. The PCM and other controllers also use input from the clutch switch for various engine control calculations, automatic braking functions, and hill hold and stop-start functions.

The P0704 code refers to the clutch switch input circuit. Consult your vehicle's service manual or All Data (DIY) for component locations and other specific information about that particular circuit specific to your vehicle.

Symptoms and severity

When a P0704 code is stored, various vehicle control, safety and traction functions may be interrupted. For this reason, this code should be considered urgent.

Symptoms of a P0704 code may include:

• Intermittent or unsuccessful engine start
• Reduced fuel efficiency
• Excessive engine idle speed
• Traction control system can be disabled
• Security features may be disabled on some models.

Causes of the P0704 code

Possible reasons for setting this code:

• Faulty clutch switch
• Worn clutch pedal lever or clutch lever bushing.
• Short circuit or breakage in the wiring and / or connectors in the clutch switch circuit
• Blown fuse or blown fuse
• Faulty PCM or PCM programming error

Diagnostic and repair procedures

A scanner, a digital volt/ohmmeter, and a service manual (or All Data DIY) for your vehicle are all the tools you will need to diagnose code P0704.

A visual inspection of the clutch switch wiring is a good place to start troubleshooting. Check all system fuses and replace blown fuses if necessary. At this time, test the battery under load, check the battery cables and battery cables. Also check the generator power.

Find the diagnostic socket, plug in the scanner and get all stored codes and freeze frame data. Make a note of this information as it may help you further diagnose. Clear the codes and test drive the vehicle to see if the code resets immediately.

If so: use the DVOM to test the battery voltage at the clutch switch input circuit. Some vehicles are equipped with multiple clutch switches to perform multiple functions. Consult All Data DIY to determine how your clutch switch works. If there is battery voltage on the input circuit, depress the clutch pedal and check the battery voltage on the output circuit. If there is no voltage in the output circuit, suspect that the clutch switch is faulty or incorrectly adjusted. Make sure the pivot clutch lever and pedal lever are mechanically working. Check the clutch pedal bush for play.

If voltage is present on both sides of the clutch switch (when the pedal is depressed), test the input circuit of the clutch switch on the PCM. This can be a battery voltage signal or a reference voltage signal, refer to your vehicle manufacturer's specifications. If there is an input signal to the PCM, suspect a faulty PCM or a PCM programming error.

If there is no clutch switch input at the PCM connector, disconnect all associated controllers and use the DVOM to test resistance for all circuits in the system. Repair or replace open or closed circuits (between clutch switch and PCM) as needed.

Additional diagnostic notes:

• Check the system fuses with the clutch pedal depressed. Fuses that may appear to be normal on the first test may fail when the circuit is under load.
• An often worn clutch pivot arm or clutch pedal bushing can be misdiagnosed as a faulty clutch switch.

How does a mechanic diagnose a P0704 code?

After using an OBD-II scanner to determine that a P0704 code has been set, the mechanic will first inspect the clutch switch wiring and connectors to determine if any damage could be causing the problem. If they are not damaged, they will check if the clutch switch is adjusted correctly. If the switch does not open and close when you hold and release the clutch pedal, the problem is most likely with the switch and/or its adjustment.

If the switch is set correctly and Code P0704 still found, the switch may need to be replaced to fix the problem.

Common Mistakes When Diagnosing Code P0704

Since this code can cause problems with starting the car, it is generally accepted that the problem is actually with the starter. Replacing or repairing the starter and/or related components will not solve the problem or clear code .

How serious is the P0704 code?

Depending on the symptoms associated with the P0704 code, this may not seem very serious. However, on manual transmission vehicles, it is important that the clutch is engaged before starting the vehicle. If the vehicle is able to start without first engaging the clutch, this may lead to other problems.

On the other hand, the car may not start at all or it will be very difficult to start. This can be dangerous, especially if the car is stuck in a traffic jam and the driver needs to get off the road.

What repairs can fix code P0704?

If the problem is caused by a faulty or damaged clutch switch, then the best repair is to replace the switch. However, in many cases, the problem may simply be a clutch switch misadjusted, or a damaged or corroded chain. Repairing the circuit and making sure all connections are properly installed can fix the problem without having to replace the clutch switch.

Additional comments to consider regarding code P0704

Whether or not the vehicle is showing any other symptoms along with the Check Engine light being on, it is important to resolve this code quickly. A faulty clutch switch can cause a number of problems, and if the Check Engine light is on, the vehicle will fail the OBD-II emissions test that is required for vehicle registration in most states.

P0704 Audi A4 B7 Clutch Switch 001796 Ross Tech

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