P0687 ECM/PCM power relay control circuit high

P0687 – OBD-II Trouble Code Technical Description

High signal level in the ECM/PCM power relay control circuit

What does the fault code mean P0687?

This Diagnostic Trouble Code (DTC) is a generic transmission code that applies to all vehicles manufactured in 1996 (VW, BMW, Chrysler, Acura, Audi, Isuzu, Jeep, GM, etc.). It indicates a high voltage detected by the powertrain control module (PCM) or other controllers on the circuit that supplies power to the PCM or on the circuit that other controllers monitor the PCM supply voltage.

To ensure proper operation, the PCM must receive a constant flow of power from the battery through the contact relay. If the voltage from the battery through this relay becomes too high, the PCM will set a P0687 code and turn on the check engine light. This problem can occur due to a faulty relay or voltage problems in the circuit.

It's important to note that while the P0687 code is common across different makes of vehicles, the causes may vary slightly depending on the manufacturer and engine design.

Possible reasons

Possible reasons for setting this code:

• The generator may be overloaded.
• Faulty PCM power relay.
• Faulty ignition switches.
• Shorted wiring or wiring connectors.

What are the symptoms of a fault code? P0687?

Code P0687 most often does not cause the engine to fail to start, but in some cases it can cause the PCM to disable itself. Although the vehicle may still start and appear to be operational, excess voltage can harm the PCM and other controllers. This code requires immediate attention.

To identify a problem, it is important to know its symptoms. Here are some main symptoms of OBD code P0687:

• Difficulty starting the engine or not starting it.
• Reduced engine power and acceleration.
• Engine misfiring.
• Check the Check Engine Light.

In most cases, the Check Engine Light will be the only symptom of a P0687 code. However, sometimes a condition may occur in which the engine will not start to prevent damage to the PCM.

How to diagnose a fault code P0687?

To identify a P0687 code, start by checking for technical service bulletins (TSBs) for your vehicle. This can save time and money since manufacturers may already know the problem and fix it. Next, check the wiring harnesses, connectors, and system components for visible damage. Pay attention to the generator to make sure it is not overloaded. Also check the battery and battery cable ends for corrosion and looseness.

To properly diagnose the P0687 code, you will need an OBD-II scan tool, a digital volt/ohm meter (DVOM), and a wiring diagram. The scanner will help you retrieve stored fault codes. Then use the wiring diagrams and connector pinouts to check the PCM power relay and its connections. Check the voltage at the appropriate terminals and ground.

If the generator is working correctly and all wires are in order, proceed to checking the circuits for short circuits. Be careful to disconnect the controllers from the wiring harness before checking resistance with the DVOM. If short circuits are detected, they must be repaired or replaced.

If you also have an alternator overcharging code, resolve its issue before addressing P0687. Remember that when replacing relays, use only relays with identical numbers. After each repair, clear the codes and check to see if they are set again.

Diagnostic errors

COMMON ERRORS WHEN DIAGNOSING CODE P0687

One common mistake when diagnosing a P0687 code is to assume too quickly that the PCM needs to be replaced to get the vehicle back on track. However, taking this step without first identifying and addressing the true cause of P0687 can be costly and ineffective. A thorough inspection and diagnosis can save a lot of time, effort and resources by accurately identifying and solving the problem. Remember that detailed diagnostics are the key to successful troubleshooting.

How serious is the fault code? P0687?

Code P0687 can have serious consequences depending on your specific situation. If it causes the vehicle to not start, the problem must be corrected before the vehicle can be driven. Even if the car still starts, it is important to understand that excessive voltage applied to the PCM can seriously damage this controller. Therefore, the longer the problem remains unresolved, the greater the risk that fixing it will require a complete PCM replacement, which can be a costly process. Therefore, it is important to take steps to diagnose and resolve the P0687 code as soon as possible to avoid more serious problems.

What repair will help eliminate the code? P0687?

There are several repair steps that can help resolve the problem associated with the P0687 code. Here are some of them:

1. Repair or replace the alternator and/or associated wiring and connectors. Problems with the alternator can cause excessive voltage, which results in a P0687 code. Check the condition of the generator and its components, as well as the wire connections.
2. Replacing the ignition switch. Defects in the ignition switch can cause trouble code P0687. Try replacing the ignition switch and make sure it functions correctly.
3. Replacing the PCM power relay. If the PCM power relay is not working properly, it may cause a high voltage problem. Try replacing this relay with a new one and make sure it functions correctly.
4. Repair or replace faulty wires or connectors between the battery, PCM power relay and the PCM itself. Wiring and connectors may be damaged or corroded, which can cause voltage problems. Check their condition and, if necessary, restore or replace.

The choice of a specific repair action depends on the diagnostic results and the problems found. When carrying out repairs, it is important to follow the recommendations of professionals and, if necessary, consult a mechanic or electronics specialist.

What is P0687 Engine Code [Quick Guide]

P0687 – Brand-specific information

Code P0687 – Electrical malfunction of the PCM (Powertrain Control Module) power system. This code can be applied to different brands of cars. To accurately diagnose and decipher this error, it is recommended to contact specialists or owners of the relevant car brands. Each manufacturer may have its own features and specifications associated with this code.