|Code||Fault Location||Probable Cause|
|P0614|| Engine control module (ECM)/transmission control module (TCM) -mismatch |
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What Does Code P0614 Mean?
SPECIAL NOTES: Non-professional mechanics should note that diagnosing code P0614 – “Engine control module (ECM)/transmission control module (TCM) –mismatch”, almost always requires the use of advanced, dealer-grade diagnostic equipment. While this code is frequently caused by the failure of the PCM, it can also be caused by a failure of the TCM (Transmission Control Module, or by wiring faults in the CAN (Controller Area Network) bus system, which cannot be accessed by cheap, generic code readers.
It should also be noted that while it may sometimes be possible to repair code P0614 on a DIY basis if the cause is obvious, attempting to diagnose/repair this code if the cause is not obvious and the required equipment, skills, and reference data are not available could result in extensive, if not always fatal damage to the application’s electrical system. For this reason, it is important to note that the information provided here is intended for general informational purposes only, and it should therefore NOT be used in any diagnostic/repair procedure for this code without making proper reference to the repair manual for the affected application.
Thus, if the few generic diagnostic steps outlined here do not resolve this code, the better option is to refer the vehicle to the dealer or other competent repair facility for professional diagnosis and repair. END OF SPECIAL NOTES.
OBD II fault code P0614 is a generic code that is defined as “Engine control module (ECM)/transmission control module (TCM) –mismatch”, or sometimes as “Engine control module (ECM)/transmission control module (TCM) – Incompatible”, and is set when a mismatch in communication (or a failure to communicate) between the PCM (Powertrain Control Module) and TCM (Transmission Control Module occurs. Note that on some applications, the code will be set and a warning light illuminated on the first failure, while on others, up to 8 failures need to occur before a warning light will be illuminated.
In the context of code P0614 and its definition, the word “mismatch” refers to a breakdown in the effective communication between the PCM and TCM. This communication happens in the form of input data that is received from multiple sensors and other control modules that is distributed to all affected control modules via the CAN bus system. Typically, the PCM acts as the “clearing house” for all received input data, but for the PCM to be able to control all engine functions effectively, it requires accurate and valid data from multiple control modules.
We need not delve into the complexities of the CAN bus system here, but it should be noted that for the engine and transmission to work as intended, the communication between the PCM and TCM needs to be in perfect harmony without any “glitches”, interruptions, or mismatches between input data sets. For instance, based on current operating conditions such as throttle position, road speed, selected shift mode, and the currently selected gear (among others), the PCM might determine that a gearshift is required. This command will be sent to the TCM, which will acknowledge the request, and initiate the gearshift.
However, should a malfunction or fault in either or both the PCM and TCM, or in the CAN bus system wiring exist that prevents effective communication between the various control modules that are affected by the gear shift request, the PCM will interpret the breakdown in communication as a mismatch between itself and the TCM, and set code P0614 as a result. Depending on the application, a warning light might also be illuminated, but in some cases, the code will be present as “pending” until the required number of failure cycles have occurred.
It should also be noted that since control modules other than the PCM and TCM are involved in the effective management of the transmission and hence, gear shifts, the breakdown in communication can occur in one or more other control modules. Typically, control modules such as the ABS Control Module, Fuel Control Module, Body Control Module and others (depending on the application) can not only note a breakdown in communication, but also “report” such a breakdown in communication to the PCM.
The image below shows a much-simplified schematic representation of how a typical automotive CAN bus system is set up. In this image it can be seen that information is shared by all controllers, but also that dedicated programming in controllers acknowledge the receipt of communicated data, as well as compare data with expected values to either accept the data, or reject it. In the case of code P0614, one or more controllers may have rejected data, or may have not received it, which will have caused the PCM to set and store the code. Note that in this diagram, “ECU 1, 2, or 3” is used to indicate electronic control modules, and not “Engine Control Unit”, which is synonymous with “PCM” (Powertrain Control Unit).
What are the common causes of code P0614 ?
Some common causes of code P0614 could include the following-
- Failed or failing PCM, TCM, or other control module. Note that control module failure is a common cause of this code
- Damaged, burnt, shorted, disconnected, or corrode wiring and/or connectors. Note that this type of damage could occur almost anywhere in the CAN bus system
- Failure to re-connect ground straps and/or other wiring after routine maintenance or repairs
What are the symptoms of code P0614 ?
WARNING: While code P0614 may not cause immediate and/or serious driveability symptoms on some applications, it does NOT mean that this code should be ignored. Serious symptoms that could affect driveability can appear unexpectedly, and in some cases the vehicle may be immobilized, which can be dangerous should this happen in heavy traffic. Nonetheless, some common and less serious symptoms of code P0614 could include the following-
- In some cases, a stored trouble code and illuminated warning light may be the only discernible symptom
- In some cases, several other, and seemingly unrelated codes may be present
- Gear shifts may be harsh, erratic, or unpredictable
- Engine may stall unexpectedly, or in an unpredictable pattern
- Idling speed may fluctuate, or the engine may not idle at all
- Idling may be rough, or erratic
- Engine may stumble or hesitate upon acceleration
- Some applications may exhibit a general loss of engine power
- Fuel consumption may increase
How do you troubleshoot code P0614 ?
NOTE: If any other codes are present long with P0614, take careful note of the order in which they were stored. Refer to the manual to determine the relationship between all other codes and P0614, and repair codes preceding P0614 before attempting a diagnosis/repair of P0614. However, misfires and poor performance are common symptoms of P0614, and unless the cause of a misfire or poor performance is obvious, these symptoms in particular are almost invariably the result of P0614, as opposed to being the cause.
Therefore, be sure to establish the relationship between all codes present, and only repair codes preceding P0641 if the manual calls for this. Diagnosing codes that accompany P00614 in a random manner will almost certainly result in a misdiagnosis, wasting a great deal of time, and unnecessarily replacing parts and components in the hope of stumbling on the solution.
Record all fault codes present, as well as all available freeze frame data. This information could be of use should an intermittent fault be diagnosed later on.
Refer to the manual to locate the PCM, and determine whether the TCM is incorporated into it, or if the TCM is a standalone module.
If the TCM is integrated into the PCM, inspect the connector for signs of damage, corrosion, or anything else that looks out of the ordinary. Wiggle the connector on the casing to check for looseness, but DO NOT disconnect the connector from the PCM casing at this point. Doing so could cause the PCM to lose vital programming or memory.
If the TCM is house separately, check the connector in the same way, but DO NOT disconnect the module from its wiring at this point.
If the connectors appear to be in perfect condition, refer to the manual to locate all system ground connection points, and check all ground connections for signs of corrosion or looseness. Clean all points as required, or remove and retighten all points.
Bear in mind that the PCM supplies the ground and reference voltage for many sensors that supply input data. Refer to the manual to determine the correct procedure to test that the PCM is actually providing the required grounds/reference voltages. If it does not, the PCM is defective and must be replaced. Bear in mind that unlike most other codes, PCM failure is major cause of code P0614, but do not condemn the PCM out of hand until it is proven to be defective.
NOTE: It is common for ground straps or other wiring to be left dangling, or not to be re-connected properly after routine maintenance or repairs. Thus, if this code appears immediately, or soon after routine maintenance or repairs, suspect disconnected wiring or damage to wiring and/or connectors in the area in which repairs or maintenance had been performed. Inspect these areas, and make repairs or connect wiring as required.
If the code still persists, perform a thorough visual inspection of all wiring (including fuses and fusible links) and especially wiring leading directly to the PCM and/or TCM. Look for damaged, burnt, disconnected, or corroded wiring and/or connectors. However, DO NOT disconnect connectors in a random fashion, since the PCM’s power supply may be interrupted which could cause the controller to lose vital programming or memory. If this happens, the PCM must be re-programmed.
If damaged wiring is found, replace wiring as opposed to making repairs in order to ensure a successful repair. However, if blown fuses/fusible links are found, do NOT replace them until the cause of the short circuit or overload is found and repaired.
If the above steps did not resolve the issue, there is nothing more the average non-professional mechanic can do diagnose and/or repair this code. From this point onwards, it becomes very difficult to trace the fault, since either one or more control modules, or the greater CAN bus system could be involved.
In simple terms, the CAN bus system consists of thousands of circuits that inter-connect all the control modules on the application, and diagnosing a fault in this complex web of harnesses requires dealer-grade diagnostic equipment, above average diagnostic skills in general, and expert level knowledge of the application in particular.
In fact, simply replacing all the wiring on some applications is often more cost effective than trying to find a fault, since testing several thousand circuits individually can take even an expert professional technician who has access to the required equipment and technical information a week or more, with no guarantee that the fault will ever be found.
Codes Related to P0614
There are no known codes that are directly related to P0614 – “Engine control module (ECM)/transmission control module (TCM) –mismatch”.