| SCP (J1850) Invalid or Missing Data for Primary Id
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Table of Contents
- What Does Code U1118 Mean?
- Where is the U1118 sensor located?
- What are the common causes of code U1118?
- Get Help with U1118
What Does Code U1118 Mean?
OBD II fault code U1118 is a manufacturer-specific trouble code, which carmakers define as SCP (J1850) Invalid or Missing Data for Primary Id. As this description is probably not reasonably intuitive and contains several abbreviations, it might need additional explanation. The SCP stands for Standard Communications Protocol, a way of communication between car components. More specifically, the protocol in question is J1850 used by many manufacturers since 1996. And lastly, there’s the phrase Invalid or Missing Data for Primary Id, whose meaning depends on the car make and model.
But, in most cases, the U1118 trouble code is set when there’s an interruption in communication with one of the vehicle’s control modules. Still, bear in mind some car makers might have a different explanation for this code.
Where is the U1118 sensor located?
Most cars made from approximately 2000 onwards have a so-called CAN-based electronics structure. CAN is short for Controller Area Network, a protocol allowing communication between various vehicle control devices. Or in simple words, this is an informational highway through which all relevant information is sent and picked up by different modules. However, all the data is coded so each control module can recognize those applicable to its operation.
For instance, when the driver presses the throttle, the readings from its position sensors are sent to the PCM, which adjusts the engine’s operation accordingly. But the PCM also shares this information with other control modules over the CAN bus. So, if the vehicle has a separate Transmission Control Unit, it will use this information to change gears if needed. Moreover, should the PCM decide full engine power is required, it could send an instruction to the air-con’s control module to shortly shut down the AC compressor.
From a technical point of view, a CAN bus is a pair of wires twisted together, which run throughout the car and connect different control modules. In most cases, it’s integrated into the vehicle’s body wiring harness.
If one of the control modules fails to communicate over the CAN, the vehicle will trigger a check engine light. When this happens, the U1118 trouble code will get stored in the diagnostic memory. Although which module is causing this differs depending on the manufacturer, there are two prominent situations. First, there is BMW, where the U1118 trouble code is set when the car fails to communicate with the TCU. Then, there are vehicles made by Peugeot and their sister company, Citroen. Here, the U1118 is triggered when there is an issue with the air-con control module. Lastly, Kia hybrid and electric cars might have this trouble code on when there is an issue with their electric water pumps.
What are the common causes of code U1118?
As said, a CAN bus is basically a wiring that plugs into various control modules, and as such, it may suffer from issues typical for components of this type. This includes broken or damaged wires, loose connectors, or corroded pins, among other things. Apart from these, owners should be aware of some specific failure points and potential causes.
The CAN network is sensitive to voltage deviations, which may manifest if the battery is on its last legs. More precisely, the U1118 trouble code could get triggered when starting the car on cold winter days. This happens because the starter motor uses a lot of battery charge while cranking, causing voltage drops throughout the rest of the car’s electronics. This issue is common with BMW cars driven in cold climates.
Air-con control module
The control module is an electronic device, and as such, it can freeze up for many reasons. This is something that air-con modules in Peugeot and Citroen cars often suffer from. And many owners have found that performing a BSI reboot could likely restore its operation. How this is done is described in this separate document.
Defective water pump
Kia Niro hybrid and electric vehicles are equipped with a separate water pump, whose job is to cool down the electric motor and corresponding components. In certain cars made in 2018 and 2019, this pump may develop a leak, which triggers U1116 or U1118 trouble codes. Depending on the situation, either the pump or its housing must be replaced. The repair procedure is described in Kia’s service bulletin SA394.
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