Error Code P2551: What It Means & What To Do?

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Check engine light flashing? Can’t comprehend the error code P2551? Well, we are here to help! All you need to know about the error code P2551 is written down here. Often, the engine control module (ECM) reduces the engine torque during shift events to improve the shift feel as per the requests of the transmission control module (TCM). Consequently, when such requests are made, the ECM replies by retarding the base ignition timing and updating it to the TCM about the completion of the request. Also, if the ECM fails to comply with the requests, it sends the TCM a message about the failure. The torque reduction request is transmitted to the ECM via communication network known as the controller area network (CAN). The CAN data between the ECM and the TCM is communicated using two circuits

It should be noted that a failure in the CAN doesn’t add to the diagnostic trouble code being stored by the ECM. A number of other codes set in before this code P2551, if incase a CAN fault occurs. The ECM stores the error code P2551 whenever it receives a torque reduction failure message from the engine control module.

What causes this problem with Torque Management Request Input Signal "B" High?

• A fault in the engine control module (ECM)
• A malfunctioning transmission control module (TCM)
• An update required in both ECM and the TCM
• Harness in the engine control module open or shorted
• A weak electrical connection running in the circuit

1. Transmission System Parts - Have you lately been experiencing rough shifts and delayed engagements? Then this is indicative of faulty transmission system parts. Log into Parts Avatar to get your hands on your new transmission system parts instantly.
2. Transmission Control Module - A distorted transmission control module can end up being the chief host inviting the error code P2551. It also performs the function of transferring power. So replacing one can be one of the wisest decisions to avoid a problematic system.
3. Engine Parts - Facing the error code P2551? Inferior quality engine parts can always be hazardous for the system also it is one of the primal causes behind the occurring of the error code P2551. Tune into Parts Avatar for supreme quality engine parts at economical prices.
4. Powertrain Control Module - A defect in the powertrain control module is likely to invite issues like a poorly running engine, increase in carbon emission, choking, stuttering and stalling of the engine. Well, to avoid these, we recommend a replacement or repair of the powertrain control module before it worsens the condition of the system.
5. Engine Wiring Connectors - Fearing an engine misfire? Then we advise you to get your engine wiring connectors changed as soon as possible. Now get your engine wiring connectors delivered right at your doorstep with Parts Avatar. Log in now!

Have you ever wondered why is it so important to know the symptoms of the problem? Well, it is extremely essential to know the symptoms of the problem in order to detect it. Keeping this in mind, let’s throw some light on few common symptoms of OBD error code P2551

Common Symptoms

• Drivability problems
• Poor fuel economy
• Engine stalling or rough idle
• Weak acceleration
• Stored trouble code with an illuminated MIL lamp
• The code may show as pending too

To correct this issue you might need to undergo few replacements for the defective parts such as:

• Repair or replace your damaged engine control module or transmission control module as per the requirements
• Make sure all the corroded or open harness in the engine control module are repaired or replaced immediately
• If required, one should also update the software in the engine control module and the transmission control module
• Fix a bad electrical connection running in the circuit 

Apart from this, you might need to replace other damaged parts too like transmission, transmission control module, engine, PCM, wiring, connectors and more. You can easily find all these parts with us. Not only that you can get these parts shipped to your door free, if your cart value happens to exceed $99.

Here are some steps which you should follow in order to diagnose this fault code:

For enhancing the automatic transmission shift feel and promoting the part’ longevity, the transmission control module requests the PCM to decrease the effective engine RPM and torque at particular shifting conditions. Whensoever the PCM gets such a request, it acts by retarding ignition timing and inputting a signal to the transmission control module to signal at the completion of the task. A failure message is input to the transmission control module, a code is set and the malfunction indicator lamp illuminates when the PCM is not successful in decreasing the degree of torque produced by the engine. It is through the controller area network or CAN, the torque reduction requests and failure messages are conveyed between the controllers. The term ‘CAN’ is representative of the a communication bus that enables multiple micro controllers to communicate with one another without the need for a host computer. Specially designed for automotive use, it is a message based protocol. Also, this CAN bus network is a complex collection of wiring harnesses and connectors utilized as a pipeline of information shared between two or more automotive control modules.

Every electrical function of the vehicle is controlled virtually by these controllers with the PCM being the chief controller. Various sensors send input data to the control modules and emit output signals to the system parts and other control modules. For example: the vehicle speed sensor sending input data to the PCM. it can be seen that this signal is systematically transferred to affected control modules that use the data to accomplish various other tasks. The data for the speed control purposes, is used by the cruise control module. The traction control module utilizes the data to manage the vehicle traction control strategy while the anti lock brake controller compares vehicle speed from the PCM with data inputs from individual wheel speed sensors to run the anti lock braking system. Well, numerous tools will be instrumental to successfully diagnose this code. Start with a visual inspection of all wiring and connectors. Make sure all the defective, loose or short circuited wiring, connectors and parts are repaired or replaced as per the requirements. To ensure success, always perform a retest after the repairs have been performed. If in case, all the system wiring, connectors and parts (including fuses) are functioning in order, the scanner (or code reader) should be connected to the diagnostic connector in order to record all stored codes and freeze frame data. Record this information as it can be extremely helpful in diagnosing the intermittent conditions that may have contributed to this code being stored. Next, continue by clearing the codes and performing the test drive to see if the code returns. This will help to ensure that whether the malfunction is intermittent or not. It should be noted that intermittent conditions can prove to be quite challenging to diagnose and in extreme cases may have to be allowed to worsen before a correct diagnosis can even be attempted. This type of code, unlike others, should sometimes be left ti professional help because of the bulk of circuitry involved. A trained mechanic with a specialized scanner (Auto hex or Tech II) may be able to determine the general area of the malfunction much more rapidly and easily than someone using a code reader and a digital volt ohmmeter. Disconnect and test every single pin of the CAN bus could prove to be extremely time and cost restricted. Also, it is important to install some type of memory saving device lest the PCM and other controllers lose their memory and require programming. Next, a specialized diagnostic CAN scanner will show pin values and control module operation without risking a meltdown. This will help in accurately diagnosing computer and circuitry problems by controlling vehicle operations while the vehicle is being operated.

Also, in order to diagnose this type of code use a digital volt ohmmeter. This would require testing thousands of circuits, independently. You should be careful as even one misplaced probe can destroy expensive control modules and will require that the vehicle should be totally reprogrammed. At most, you should perform a continuity test after all control modules are detached, and this could literally require 40-hours or more varying according to the vehicle. A number of applications have up to 18 separate control modules installed. Begin with a careful inspection of all the circuitry and connectors and fuses if you want of tackle this task. Test the control module ground circuits for continuity with battery ground. These types of codes are usually caused by damaged or disconnected system grounds. Also, an auxiliary ground cable can be extremely helpful in diagnosing system ground abnormalities. The engine and transmission ground cables, straps, and wires are left dangling after repairs are performed at times. Search for loose or burnt electrical connectors that may increase circuit resistance and cause these types of codes to be stored. Acquire a CAN bus system wiring diagram and/or pin out value chart. Then make use of the digital volt ohmmeter to test continuity between individual controller connectors. Then compare the results with the manufacturer's referenced values and repair loose or shorted circuits as per the requirements. Often, it is much more thrifty to restore damaged wiring rather than attempting to remove it from an intricate web of wiring harnesses.

Common mistakes when diagnosing the error code P2551

The mechanic should be careful while clearing the engine control module codes before checking the freeze frame data for the main failure so that it isn't duplicated and repaired. Also, a failure to clear the ECM codes after the codes are fixed should also be prevented. Then, one shouldn't simply replace the O2 sensor without even checking the failure of the heater circuit as it could even be triggered due to an intermittently short circuited wire in the harness.

P2550 - Torque Management Request Input Signal "B" Low