ECUReset (0x11)

What is ECUReset (0x11)?

ECUReset is the UDS service that restarts an ECU under tester control. The sub-function byte selects the reset type. The ECU sends the positive response first and then performs the reset, so the tester can see the acknowledgement before the server disappears for a moment.

A normal exchange:

Direction	Bytes	Meaning
Request	11 01	hardReset
Positive response	51 01	reset accepted, ECU reboots
Negative response	7F 11 33	securityAccessDenied

Other typical negative responses are 7F 11 7F (serviceNotSupportedInActiveSession, reset requested from the default session when the ECU requires the extended session), 7F 11 12 (subFunctionNotSupported for an unknown reset type), 7F 11 13 (incorrectMessageLengthOrInvalidFormat) and 7F 11 22 (conditionsNotCorrect, for example the engine is running).

Where is it defined?

ISO 14229-1:2020 defines ECUReset (0x11) in the Diagnostic and communication management functional unit. The standard lists the reset types, the response format including the powerDownTime byte for rapid power shutdown, and the rule that a reset returns the server to the default session. On CAN the transport is ISO 15765-2.

What it means in practice

Most ECUs allow ECUReset only in the extended or programming session, and often behind SecurityAccess, because an uncontrolled reset of a running controller is dangerous. In validation, engineers check:

• the service answers only in the sessions and at the security level the specification allows;
• a wrong length (11 alone or 11 01 00) gives NRC 0x13;
• an unknown sub-function gives NRC 0x12;
• the ECU actually comes back after the reset and in the default session;
• conditions such as a running engine correctly produce conditionsNotCorrect instead of a reset.

On the bench, reset handling is where session bugs surface. We regularly see ECUs that hang or need a power cycle after a soft reset, and ECUs that do not drop a security unlock across a keyOffOnReset, which they must.

How AutoST tests it

AutoST flags ECUReset during enumeration as a risky service, records in which sessions it answers and with which negative response codes, and confirms the ECU returns cleanly to the default session. In fuzzing, a TesterPresent liveness check after every iteration catches an ECU that reset or hung in response to a payload, and the exact payload that preceded it is stored so the reset can be replayed.