Serial data circuit is used to communicate information between systems. Each system on the serial data line is assigned its own recognition code, which is used to identify which system is communicating. Systems periodically send a State of Health (SOH) message to other systems. If those systems fail to send an SOH message back, a corresponding DTC will be set. Also, any system that cannot communicate properly will set the corresponding DTC.

DTC U1255 will set when BCM does not receive a SOH message response for one second from PCM or IPC when ignition is first turned on. DTC U1255 will also set when BCM detects an open or short in serial data line circuit for one second. PCM will not allow fuel enable processing to occur, which may cause vehicle to display a "engine cranks, but does not run" condition. No driver warning message will be displayed.

DTC U1255 requires an ignition cycle to change from current to history. If conditions for malfunction no longer exist, history DTC will clear after 50 consecutive ignition cycles. DTC U1255 will also clear when conditions no longer exist, or when IPC or scan tool is used to clear codes.

NOTE: If DTC U1255 is a history code, problem may be intermittent. Wiggle wires while performing the following test.

When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

• You smell fuel, burning insulation, or see smoke.

• Brakes feel soft, pull hard to one side, or make grinding noises.

• The engine overheats, stalls repeatedly, or misfires under load.

• You are missing required tools, torque specs, or safe lifting equipment.

• You are not confident in the next step or safety outcome.

Safety Warning

DTC U1255: Serial Data Line Malfunction: Notes

Use the Manual With the Right Hardware

When to See a Mechanic