P26C8: a received warning request points to another controller’s findings

P26C8 is a received malfunction-indicator request in this GM example. The engine controller observes a serial-data message indicating that the fuel-pump control module has requested a warning. The generic chassis-control wording does not mean that the ECM independently diagnosed a particular pump or shutter failure.

Read the controller that originated the request

The source specifically notes that the fuel-pump control module also controls the active grille shutters in the documented application. Its name therefore does not identify which of its functions generated the underlying fault. The originating module's own codes and records are essential evidence.

P26C8 also differs from a lost-communication diagnosis: this monitor requires receipt of a new CAN message carrying the request. Replacing a module because “communication” appears in the strategy would ignore that the controller actually received the relevant information.

The request is not the root-cause code

The table requires ignition on for more than three seconds, a new message and the remaining enable conditions. It lists a one-second failure condition with a once-per-trip evaluation. Those details describe how the request is recognized; they do not identify the fault that prompted it.

A technician should preserve codes from both controllers and investigate the originating module through the correct application-specific procedure. There is no universal fuel-pump or grille-shutter replacement rule in this summary. After the underlying condition is addressed, verify that the requesting module no longer reports its fault and that the ECM receives the appropriate state during an eligible evaluation.

Source and applicability

GM 2015 15OBDG04 serial-data MIL-request monitor. Only the cited monitor and calibration are described; per-code vehicle and engine applicability has not been established.

15OBDG04 Engine Diagnostics, physical PDF page 131.