P0650 – Malfunction indicator lamp (MIL) -circuit malfunction

By Reinier (Contact Me)
Last Updated 2017-01-31
Automobile Repair Shop Owner

Table of Contents

1. What Does Code P0650 Mean?
2. What are the common causes of code P0650 ?
3. What are the symptoms of code P0650 ?
4. How do you troubleshoot code P0650 ?
5. Codes Related to P0650
6. Get Help with P0650

What Does Code P0650 Mean?

OBD II code P0650 is a generic code that is defined as “Malfunction indicator lamp (MIL) -circuit malfunction”, and is set when the PCM (Powertrain Control Module) or any other supporting controller in the CAN (Controller Area Network) bus system detects a problem in the MIL (Malfunction Indicator Lamp) itself, or in its control circuit. Note that while “MIL” usually refers to the “CHECK ENGINE”, or “SERVICE ENGINE SOON” lamp, code P0650 can also apply to other warning lights on some applications.

In practice, warning lights in vehicles serve to warn the driver that something is wrong, or something is in the process of going wrong in one or more of the hundreds, if not thousands of circuits that control virtually every aspect of a vehicle’s operation. Connecting all of these circuits are controllers that receive data from dozens of sensors around the vehicle through still more circuits.

Moreover, all controllers (control modules), of which there can be as many as 30 or sometimes more on a high-end application, are interconnected via yet more circuits that are all in their turn interconnected through the CAN (Controller Area Network) bus system, with the PCM serving as the “clearing house”, or central processing unit that ultimately controls and/or monitors the operation of all other controllers, which include, but are not limited to the-

• fuel control module
• alternative fuel control module
• body control module
• ABS control module
• instrument panel control module
• fuel injection control module
• turbo control module
• anti-theft module
• cruise control module
• traction control module
• proximity alert module, and the
• climate control module.

We need not delve into the complexities of the CAN system here, beyond saying that all control units are connected by it, and that it allows all controllers to communicate with each other, sometimes without involving the PCM, although the PCM is involved in most communications that go through the CAN bus system.

An example of a typical information exchange would be when the PCM receives a signal from say, the vehicle speed sensor. This data is forwarded to all other controllers that use this information to perform other, but related tasks, such as the cruise control module for the purpose of monitoring/controlling the vehicles’ speed, and the ABS controller for the purposes of arming the traction, and stability control systems in conjunction with the wheel speed sensors.

The above example may be an oversimplification, but it serves to illustrate the point that effective communication between all affected controllers is crucially important for the safe operation of a vehicle. Thus, should a malfunction occur anywhere between the controllers that are involved in the above example, the fault will be detected by the controller in whose “jurisdiction” the fault occurred, but it may be detected by one or more other controllers as well.

Regardless of which controller detected the fault though, the fault data will be forwarded the PCM, which will set the relevant codes, which may or may not illuminate a warning light. However, to complicate matters, many controllers have the ability to set fault codes as well, and in a fully functional MIL system, the relevant warning lights will be illuminated when a fault occurs, depending on the fault, and the number of failure cycles required before a warning light illuminates.

If however, the dedicated MIL control circuits of either the PCM or any other controller are affected by a failure or malfunction, the PCM will be made aware of that fact, and it will set code P0650 specifically to indicate that there is a problem/failure/malfunction in the MIL circuits of a controller, as opposed to indicating a fault that affects the operation of the vehicle.

The image below shows a code reader displaying code P0650. In this image, the relevant code is circled in black for clarity, but note that even though this professional-grade scanner displays a sub code (04), it does not display the controller, or the system in which the MIL circuit failure had occurred. Making matters worse is the fact that cheap, generic code readers generally never display as much as a sub-code, which more often than not, leaves the average non-professional mechanic with no choice other than to refer the vehicle for professional diagnosis and repair.

What are the common causes of code P0650 ?

Common causes of P0650 could include the following-

• Damaged, burnt, shorted, disconnected, or corroded wiring and/or connectors almost anywhere in the CAN bus system. Note that while blown MIL indicator bulbs can also set this code, we do not recommend that non-professional mechanics test for this since a simple, or even honest mistake during this test could destroy sensitive circuitry in the PCM and/or other controller(s).
• Improperly tightened ground straps or wiring as the result of sloppy maintenance or repair work.
• Failures or malfunctions in the MIL-associated circuitry of the PCM or other controller. Note that this is relatively rare, and merely replacing controllers (which often require reprogramming) will almost never resolve code P0650.

What are the symptoms of code P0650 ?

Possible symptoms of P0650 could include the following-

• Stored trouble code. Note that this code could also be stored as “pending”.
• Depending on the application and the nature of the problem, the MIL lamp could flash, or remain lit after self-diagnostic tests are completed upon switching on or starting the vehicle.
• In some cases, and again depending on the problem and the application, the MIL lamp may not illuminate at all.

How do you troubleshoot code P0650 ?

SPECIAL NOTES: Unless the cause(s) of P0650 is/are obvious, diagnosing this code requires professional grade diagnostic equipment, above average diagnostic skills in general, and expert level knowledge of the application in particular, because the causes of this code are often buried deep in the CAN system.  

Non-professional mechanics are therefore advised NOT to attempt a diagnosis and repair of this code and especially not in cases where there are no visible or obvious signs of damage to wiring. Haphazard or ill-considered diagnostic methods performed in the hope of stumbling on the problem will almost certainly result in extensive, if not fatal damage to the applications’ electrical system in general, and to one or more control modules in particular.

Nonetheless, it is sometimes possible to resolve this code by non-professionals, but take note that if the few generic steps outlined below does not resolve the problem, the wisest option is to refer the vehicle for professional diagnosis and repair. END OF SPECIAL NOTES.   

Step 1

Record all fault codes present, as well as all available freeze frame data. This information could be of some use should an intermittent fault be diagnosed later on.

NOTE: Make a point of checking the system voltage t this point, since abnormal system voltages can (and do) cause all manner of codes, failures, and malfunctions, of which code P0650 is a prime example.

Step 2

If the system voltage checks out, clear the code, and operate the vehicle for at least one drive cycle to see if the code returns. Bear in mind though that if this code is stored as “pending” on some applications, as many as eight failure cycles could be required before the code becomes active.

Thus, if the code returns, it could be as a result of an intermittent issue, or it could be “hard” failure, which will be indicated by an active code. If the code is active, proceed as follows, especially if any repairs or maintenance had been performed on the vehicle in the recent past-

Refer to the manual to identify and locate all ground connection points and straps. It often happens that wiring is not connected properly during or after repairs, and since not all control modules are grounded in or by the PCM, an improperly connected earth wire or strap could cause this code or contribute to its setting.

Make repairs as required, clear the code, and rescan the system to see if the code returns.

Step 3

If the code persists, perform as thorough an inspection of all visible wiring and connectors as accessibility allows. Look for damaged, burnt, shorted, or disconnected wiring and/or connectors, and especially near hot exhaust components, where wiring passes through bodywork, or where it is likely that wiring might chafe against engine or body parts.

If such damage is found, make repairs as required, clear the code, and rescan the system to see if the code returns.

NOTE: Pay particular attention to the condition of connectors during this step. Look for obvious signs of damage caused by overheating as a result of poor connections, or for corrosion that could also cause poor connections and high resistances. Make repairs as required, or replace wiring/connectors as required, and rescan the system after clearing the code to see if the code returns.

WARNING: Do NOT disconnect the battery or connectors randomly, or in a willy-nilly fashion. Doing so could interrupt the power supply to one or more control modules, which could cause affected modules to lose vital programming or memory, which will make it even more difficult to find the real cause of this code. Always consult the manual for the application being worked on for detailed information on the possible results of disconnecting any connector, before disconnecting anything from anything else.

If there is any doubt about the possible negative effects of disconnecting connectors to check for damage or corrosion, install a memory saving device to keep critical systems powered up, but be sure to only install devices that are approved by the vehicles’ manufacturer- and then only in strict accordance with the instructions provided in the manual.

Step 4

Be aware that if the steps outlined above did not resolve the issue there is very little else the average non-professional mechanic can do to resolve the code, and we therefore do NOT recommend that unskilled persons attempt ANY other diagnostic procedures beyond Step 3.

From this point on, a skilled technician requires dealer-grade diagnostic equipment to isolate the part of the CAN bus system that is most likely to contain the fault, which he may or may not be able to do depending on the application, and the exact nature of the problem.

Failing to isolate the problem means that each of the several thousand circuits in the CAN bus system must be tested for resistance, continuity, ground connectivity, and reference voltage(s) individually. This is a process that could take a highly skilled technician a week or more to complete, hence the recommendation that the vehicle be referred to the dealer, or other competent repair shop for professional diagnosis and repair.

Codes Related to P0650

There are no known codes that are directly related to P0650 – “Malfunction indicator lamp (MIL) -circuit malfunction”.

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