U1262 – SCP (J1850) Communication Bus Fault

Reinier

By Reinier (Contact Me)
Last Updated 2017-08-26
Automobile Repair Shop Owner

Trouble CodeFault LocationProbable Cause
U1262 SCP (J1850) Communication Bus Fault Power supply, Wiring, Fuses, Instrument cluster input sensors, PCM, GEM

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What Does Code U1262 Mean?

OBD II fault code is a manufacturer specific code that is defined by car maker Ford as U1262 – “SCP (J1850) Communication Bus Fault”, or sometimes as “SCP (J1850) Communication Bus Fault – Instrument Cluster” and is set when the PCM (Powertrain Control Module) detects a communication failure between itself and HEC (Hybrid Electronic Cluster). Note that “SCP” in this definition means “Serial Communications Protocol”, which is Ford’s interpretation of the SAE (Society of Automotive Engineers) J1850 standard.

In simple terms, Serial Communication Protocol refers to the flow of data across a network that is more commonly referred to as a “bus”. In this case, the bus is the communication system across which the PCM delivers input data to all the instruments, warning lights, and other indicators on the instrument cluster. Typical information that flows across the bus involves vehicle speed, RPM (engine speed), engine/transmission temperatures, system voltages, and warning lights that indicate the status of various systems and features that may be fitted to the particular application.

The image below shows part of a typical Ford instrument cluster printed circuit. Note that apart from replacing this circuit board, it is generally not possible to repair Ford instrument clusters on a DIY basis.

Where is the U1262 sensor located?

The location of the instrument cluster is self-explanatory. However, the PCM on most Ford models is located under the hood on the left-hand side of the firewall (as seen from the driver’s seat), while the GEM (Generic Electronic Module) is usually located under the dashboard close to, or behind the radio.

What are the common causes of code U1262?

Some common causes of code U1262 could include the following-

  • Interrupted or erratic power supply to the PCM
  • Damaged, burnt, shorted, disconnected, or corroded wiring and/or connectors
  • Blown fuses or fusible links
  • Defective or failed sensors that supply relevant input data to the instrument cluster via the PCM
  • Failed or failing control modules that could include the PCM, and/or the GEM (Generic Electronic Module). Note though that control module failure is relatively rare, and the fault must be sought elsewhere before any control module is rare.

What are the symptoms of code U1262?

Some common symptoms of code U1262 could include the following-

  • Stored trouble code and an illuminated warning light
  • Several other codes may be present
  • Depending on the exact nature of the problem, one or more(or all) warning lights may be illuminated permanently, or no warning lights may illuminate during self-test cycles
  • Engine may crank without starting
  • Instruments such as the fuel gauge may display incorrectly, erratically, or may not work at all

What are common solutions to code U1262?

The possible solutions to code U2162 are many and varied, and could include the inspection and repair/replacement of several of the components and systems listed below.

Mechanical:

  • Engine oil filter
  • Engine oil level
  • Oil pump
  • Engine oil level
  • Oil pressure switch
  • Engine coolant level
  • Coolant thermostat
  • Fuel gauge
  • Collapsed or damaged fuel tank
  • Fuel tank filler pipe/hose
  • Indicated fuel level
  • Fuel/EVAP lines
  • Fuel tank filler cap
  • Fuel filter (external to the fuel tank)
  • Fuel tank
  • Door, hood, and trunk adjustment

Electrical:

  • Fuse(s)
  • Bulb(s)
  • LED(s)
  • Wiring harness
  • Electrical connector(s)
  • Sensor(s)
  • Instrument cluster
  • Instrument cluster printed circuit

How serious is code U1262?

Code U1262 must be considered as serious, since functions such as engine/transmission coolant temperatures, and the fuel level may not be displayed correctly, if they are displayed at all.

How safe is it to still drive the car with code U1262?

Since the vehicle’s road speed may not be displayed accurately, it may not be safe to drive the vehicle while code U1262 remains unresolved.

How difficult is it to repair code U1262?

Non-professional mechanics should note that resolving this code can vary from moderately difficult, to extremely challenging, since in many cases, removal of the entire instrument cluster is required to gain access to the instrument cluster wiring connector.

Also note that tracing an open circuit in the bus system involves back-probing and testing every circuit that enters and leaves the instrument cluster. To do this successfully requires a repair manual that includes a wiring diagram, pin out charts, and reference data for that particular application. Also required is a good quality digital multimeter, as well as suitable back-probing adapters to avoid damaging electrical connectors.

Moreover, in most cases, “U” codes cannot be diagnosed accurately with cheap, generic code readers that cannot access communication bus systems. If suitable diagnostic equipment is not available, the better option is to refer the vehicle to the dealer or other competent repair facility for professional diagnosis and repair.

What are the common mistakes when repairing code U1262?

Instrument clusters and/or control  modules, including PCM’s are often replaced in error (or desperation) when the fault is more likely to involve open circuits, damaged or short circuited wiring, defective relays, or blown fuses.

Note that control modules should never be replaced merely because a “U” code (module-to-module communications code) is present. These codes do not necessarily indicate a problem, since in some cases “U” codes can set as the result of normal self-test or diagnostic functions performed by the OBD II diagnostic system.

How do you troubleshoot code U1262?

Step 1

Record all fault codes present, as well as all available freeze frame data. This information can be of use should an intermittent fault be diagnosed later on.

NOTE: If other codes are present, note the order in which they were stored. Also determine their relationship with code U1262, and if any codes relate to the power supply of the PCM, investigate and resolve these codes before attempting a diagnosis of U1262. Failure to do this will result in a misdiagnosis and the distinct possibility that parts and components will be replaced unnecessarily.

Step 2

Once it is certain that the PCM’s power supply circuits are all in perfect working order, and that all related fuses and fusible links are intact, attempt to clear all codes to eliminate the possibility that this code was set as the result of normal diagnostic processes. If the codes clear and the vehicle can be driven, complete at least one complete drive cycle to see if any codes return.

NOTE: If blown fuses are found, do NOT replace them until the short circuit(s) or voltage overload(s) that caused them to blow have been found and repaired.

Step 3

If the fault persists, refer to the manual to determine the correct procedure to follow to remove the instrument cluster from the dashboard without breaking or damaging anything. Note that poor electrical connections in the instrument cluster connector is a common cause of code U1261, but the only way to gain access to the connector is to remove the cluster.

Step 4

Inspect the electrical connector, the instrument cluster, as well as the cluster printed circuit board for obvious signs or evidence of electrical or mechanical damage. Note that if the cluster itself shows signs of internal short circuits, the better option is to replace the cluster to ensure reliable operation of all instruments and indicators.

WARNING:  Be aware that the instrument cluster is a programmable module, which means that the replacement cluster must be configured and integrated into the CAN bus system. Note that the required integration/configuration processes vary between models and trim levels, so refer to the manual to determine the correct procedure to follow to verify the success (or otherwise) of the process.

Step 5

Inspect the electrical connector for evidence of damage and/or corrosion. Pull the connector apart to inspect the pins/terminals in both halves, but resist the temptation to make repairs if pins are damaged or corroded. In these cases, the better option is to replace the connector or the relevant wiring harness to ensure proper operation of the cluster.

Step 6

Note that if the connector is undamaged, the diagnostic procedure becomes specific to the model from this point onwards.

Note that some indicators on the cluster have multiple inputs; for instance, the brake system warning light may receive input data from the brake fluid reservoir, the parking brake levers’ position switch, and in some cases, the brake light switch. In practice, this means that each circuit must be tested individually for resistance, ground integrity, and continuity.

NOTE: if the available code reader has control functions, initiate the diagnostic mode. This will test every circuit in the cluster, which saves a lot of time. However, on most, if not all models it is possible to initiate the self diagnostic mode manually without a code reader; refer to the manual to determine the appropriate steps on how to do this on the affected application.

Step 7

If the self-test mode reveals a problem, inspect the relevant circuit(s) for signs of damaged, shorted, disconnected, burnt, or corroded wiring and/or connectors between the cluster and the relevant control module. Make repairs or replace wiring as required if such damage is found.

Step 8

Note that if the self-test mode does not initiate or complete, it becomes necessary to test each circuit individually, in strict accordance with the instructions provided in the manual.  Be aware though that this process can take many hours, and that great care MUST be taken during the entire process to avoid inadvertently causing short circuits that can damage wiring, components and/or control modules.

Test one circuit at time to avoid confusion and/or misdiagnoses. Compare all obtained readings with the values stated in the manual, and make repairs or replace wiring as required to ensure that all electrical values fall within the ranges specified by the manufacturer.

NOTE: To minimize the risk of damaging control modules, be sure to disconnect all wiring from the relevant control module(s) during resistance or continuity tests.

Step 9

If all electrical circuits check out but the fault persists, suspect either a defective instrument cluster or one or more failed control modules. Note though that it is far more likely far the cluster to have failed, so refer to the manual to determine the correct procedure to test the resistance/continuity of ALL testable circuits in the cluster.

Note that it is NOT advisable to attempt repairs of a Hybrid Electronic Cluster on a DIY basis. If testing reveals evidence of an internal failure of any part of the cluster, the better option is to replace the cluster, rather than attempting repairs that may or may not be effective.

Step 10

Once all repairs are complete, initiate the cluster self-test mode to verify the success of the repair. However, if the fault persists, refer the vehicle to the dealer or other competent repair facility for professional diagnosis and repair, since it may become necessary to test/replace either control modules, or large sections of the vehicles’ wiring.

Codes Related to U1262

There an known codes for Ford that are directly related to U1262 – “SCP (J1850) Communication Bus Fault – Instrument Cluster”

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