SCP (J1850) Invalid or Missing Data for Primary Id

OBD II fault code U1112 is a manufacturer-specific trouble code that is defined by carmakers Ford and Mazda as “SCP (J1850) Invalid or Missing Data for Primary Id”, and is set when the PCM (Powertrain Control Module) detects the failure of a control module to identify itself while transmitting data over a communications network.

Note the following in the context of this code- “SCP” stands S tandard C ommunications P rotocol “Primary ID” refers to a control module that controls, monitors, or manages a clearly defined set of functions, but note that in the case of code U1112 on Ford and Mazda applications, that control module is not identified “J1850” is a shortened expression of SAE Standard J1850, which is the standard that describes a serial communications protocol used by Ford and Mazda since 1996 This protocol uses a pulse width modulated signal to transmit data at average speeds of up to 41.6 kilobytes per second, although some versions of this protocol can transmit data at higher rates There are currently several hundred generic as well as manufacturer-specific trouble codes in common use that include the phrase “Invalid or Missing Data for Primary Id”.

In some cases, the area of concern is indicated by information that may include the name of a specific control module and/or system, but in many more cases, no information identifies the area of concern. See the section on possible causes of code U1112 for more details All modern vehicles use complex serial communications systems to distribute information about the operational status of dozens of systems and operating parameters between control modules.

While there are significant design and technical differences between the various communications protocols and system topologies (system architectures) between vehicle manufacturers, all serial communications systems have the function of maintaining communications between control modules to ensure the safe and efficient operation of the vehicle. One example of this need would be the distribution of information about the rates at which all the wheels rotate.

In practice, this information is collected by wheel speed sensors that transmit the data to the ABS control module, which then relays it to the PCM and other control modules such as Traction-, and Stability Control Modules, since these modules use the ABS system to maintain and/or restore the vehicle’s stability.

In terms of practicalities though, each control module that shares information with other modules has a unique identifying code, which code is included in all data transmissions made by that control module. Moreover, all control modules are programmed with the identifying codes of all other control modules on a given network, and this information is compared during the transmission and reception of data.

Thus, all control modules always “know” which control module transmitted which data, regardless of the system involved. Moreover, all control modules that share a network also “know” what type of information all other control modules on that network are supposed to transmit. Put in another way, all control modules are programmed to transmit the operating parameters of the system, part, or component they control, manage, or monitor.

These parameters are transmitted in strictly organized/structured messages, and all monitored parameters must be included in all data transmissions for the transmitted data to be valid. Therefore, to maintain a serial communication system’s integrity, all receiving control modules that share that network perform “checksum” checks, in which all expected information must be included, along with the transmitting module’s unique identifying code.

If all expected information is received, all receiving modules will acknowledge the data transmission to the transmitting module in a structured message that confirms that the received information agrees with the information that was expected. However, in cases where a transmitting control module