|Code||Fault Location||Probable Cause|
|P0601|| Engine control module (ECM) -memory check sum error |
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What Does Code P0601 Mean?
OBD II fault code P0601 is defined as “Internal Control Module Memory Check Sum Error”, and is set when the PCM (Powertrain Control Module) detects either a breakdown in communication between itself and one or more supporting control modules, or between two or more supporting control modules. In all cases, the PCM acts as the central or main controller.
When a breakdown in communication occurs in any area of the CAN system, a code will be stored and a warning light will be triggered. However, depending on the application, several drive cycles (up to 8 in some cases) may be required to before a code is stored and a warning light is triggered.
The CAN (Controller Area Network) typically includes control modules for systems such as, turbo boost control, ABS brakes, the instrument panel, anti-theft/security system, cruise control, fuel management, transmission control, climate control, proximity control, body control, and safety systems such as traction and stability control. Note that this list is not exhaustive, and that the actual number of control modules that make up the CAN system is make and model specific.
In practice, the CAN system monitors and controls every aspect of a vehicle’s operation by means of a system that allows all the microprocessors and controllers in a vehicle to constantly exchange messages and signals between themselves, and the sensors/systems they control. This is accomplished by the complex interconnection of all affected wiring harnesses to create a “distribution pipeline” to carry input and signal voltages from, and to various sensors, components, systems, other controllers, and ultimately to and from the PCM.
To illustrate how the system works (albeit in a grossly over simplified manner), imagine that the PCM receives a signal from the vehicle speed sensor. Provided that the signal is valid and that the CAN system is in good working order, the PCM will make the signal available to the-
- cruise control system (if fitted) for speed control purposes,
- ABS brakes system, which will compare the signal and the actual vehicle speed to information collected from the wheel speed sensors to arm the brake, stability and traction control systems,
- fuel management system via the throttle position sensor (and others) for the purposes of calculating an appropriate fuel delivery strategy,
- transmission control system to regulate efficient shifting,
- and the proximity warning system, among others.
NOTE: The above example of CAN bus operation is not definitive, and is meant for general informational purposes only. It should therefore NOT be used in any diagnostic procedure relating to the CAN bus system.
The image below shows a simplified approximation of which systems on a modern vehicle are interconnected by the Controller Area Network. Note that only critical systems are shown in this image. Other, non-critical like audio, GPS, lighting, security/anti-theft, and others are not shown.
What are the common causes of code P0601 ?
The number of possible causes of P0601 is almost directly proportional to the complexity of the CAN bus system. Nonetheless, some causes occur more often than others, with the following being the most likely-
- Damaged, burnt, shorted, or corroded wiring and connectors.
- Open circuits.
- Poor controller ground connections.
- Defective drivers in one or more controllers.
- Defective electronic components in controllers.
- Damage to controllers caused by voltage spikes or low battery voltages.
- Short circuits caused by water ingress during flooding events.
- Unlike most other codes, a defective PCM is a distinct possibility with code P0601.
What are the symptoms of code P0601 ?
In some cases there may be no symptoms present other than a stored trouble code and an illuminated warning light. However, where drivability issues are present, the symptoms are almost always make and model specific. Typical symptoms could include the following-
- Harsh, erratic, or unpredictable shifting.
- Reduced fuel economy.
- Surging or hesitation upon acceleration.
- Poor acceleration and loss of power.
- Frequent engine stalling.
- Hard starting.
- Rough or erratic idling.
- Illuminated warning lights for the ABS, traction control, stability control, air bags, or collision warning systems. Note that not all these warning lights will always be illuminated on all applications.
NOTE: On applications that require multiple drive/fault cycles before a warning light illuminates, but code P0601 is stored, the code should NOT be ignored. In these cases, the code is pending, and it may illuminate one or more warning lights at any time.
How do you troubleshoot code P0601 ?
WARNING #1: Due to the extreme complexity of the CAN bus system, non-professionals should ideally NOT attempt to diagnose and repair any codes that relate to this system. Some applications have up to 18 or more controllers that are interconnected with literally hundreds of circuits that share several thousand individual connections and connector pins. Moreover, generic code readers are NOT able to even indicate an area of the system in which a fault might be present, and even though specialized diagnostic equipment is available that can isolate certain parts of the CAN bus system, using this functionality to best effect requires expert knowledge and exceptional diagnostic skills. For instance, one accidental contact with a probe on an incorrect connector pin at the wrong time can destroy the memory on one or more controllers that may, or may not be reprogrammable.
Note that even specialists usually require anything from 40 to 50 hours (or more in some cases) to trace a fault in the CAN bus system, which makes this process extremely expensive, and even then there are no guarantees that the root cause of the problem will ever be found and repaired.
WARNING #2: Even if you are confident that your diagnostic abilities and knowledge of automotive electronics are up to this mammoth endeavor, we do NOT recommend the use of generic code readers and multimeters to diagnose this code. At the very least, you need a scanner that can communicate with the CAN system via protocols such as SAE J1939, GMLAN, OBD II, SAE J1587 and LIN, since these protocols determine the manner in which data in the system is received, formatted, and transmitted, as opposed to how fast the data is transmitted. If you do not have access this class of diagnostic equipment, refer the vehicle for professional diagnosis and repair.
Warning #3: Note that diagnosing this code will require the disconnection of some or all controllers from the PCM, an action that could cause one or more controllers to lose their memory or programming. To prevent this, an approved memory saving device MUST be used in accordance with the instructions given in the manual.
Assuming that suitable diagnostic equipment is available, record all fault codes present as well as all available freeze frame data. This information can be crucially important in determining the order in which codes were generated and stored.
NOTE: When diagnosing code P0601 and there are other codes present such as those relating to misfires, rich/lean exhaust issues, fuel injection problems, transmission trouble, or almost any other driveability-related code, it is important to recognize that these codes are almost certainly the result of a communication failure in the CAN bus system, rather than indicators of problems in the systems to which the codes relate.
Therefore, always follow the rule that says codes must be diagnosed and repaired in the order in which they were stored. Thus, if code P0601 occurred first, it will be stored first, meaning that resolving P0601 will usually resolve all the other codes as well. Freeze frame data is the best tool to determine which code came first- P0601, or the host of other possible codes.
Perform a thorough visual inspection of all points where wiring terminates against the body work. These points are ground connections, and it is common to find loose connections, or even ground straps hanging loose after unrelated repairs had been done. Consult the manual on the locations of all ground connections, and ensure that all connections are tight and secure.
If poor ground connections were found and repaired, clear all codes, and rescan the system to see if any codes return. In some cases, it is possible that some controllers may need to be reintegrated or even reprogrammed after a communication failure. Consult the manual on the correct procedures for doing this.
NOTE: Many, if not most controllers have external ground connections that need to be secure for the controllers to work.
If all ground connections are secure, perform a thorough visual inspection of all wiring on the vehicle. Note that this inspection may require removal of the dashboard, seats, carpets, and even trim panels to gain access to all wiring harnesses.
Look for obvious signs of damaged, burnt, shorted, or corroded wiring and/or connectors. Be aware though that some kinds of damage may not be visible without removing all of the insulating material wrapped around the wiring harness(es). However, use extreme caution when removing insulation to prevent creating damage where there was none before.
If any damage is found, resist the temptation to repair wiring to prevent continuity, resistance, and other issues caused by poorly executed repairs. In these cases, the better option is always to replace the affected section of the harness with an OEM replacement.
Clear all codes, and rescan the system after replacing wiring to see if any codes return. In some cases, it is possible that some controllers may need to be reintegrated or even reprogrammed after a communication failure. Consult the manual on the correct procedures for doing this.
If no damage to the wiring is found but the code(s) persist despite performing the above steps, one option may be to replace the entire electrical harness with an OEM replacement. However, this is not guaranteed to resolve the problem, since the issue may be with a controller.
Typical problems with controllers include defective drivers, “memory loss”, and/or blown components due to any number of causes. For this reason, we do NOT recommend replacing the entire harness until exhaustive diagnostic tests had been performed on all controllers, including the PCM where this is possible.
NOTE: It is worth pointing out again that no code reader, regardless of its level of sophistication, can accurately pinpoint a problem in the CAN bus system. The best even a skilled operator can hope for is to narrow down the field of search somewhat, which means that if the problem persists beyond Step 3, the vehicle should be referred to a specialist for professional diagnosis and repair.
Codes Related to P0601
- P0603 – Relates to “Internal Control Module Keep Alive Memory (KAM) Error”
- P0604 – Relates to “Internal Control Module RAM Error”
- P0605 – Relates to “Internal Control Module ROM Error (Module Identification Defined by SAE J1979)
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