Safety Mode is a condition where the Z’s ECU changes specific settings in order to protect the engine. It is enabled for a variety of reasons, and there are a few different ways it can manifest itself.
Different Safety Modes
Depending on the cause, the ECU has a few different safety routines it can enter to protect the engine.
Detonation (“Safety Boost”)
If the ECU detects detonation through the detonation sensor, it enters a mode commonly referred to as “safety boost.” It switches to “low octane” fuel/timing maps, which use more fuel and a more retarded timing condition to help prevent the engine from detonating. In turbocharged models, it also applies power to the wastegate solenoids, which open to allow more boost pressure to reach the wastegates. This causes them to open at a maximum of ~7psi, rather than ~9.5psi.
This safety mode is also enabled immediately if the ECU throws Code 34, which indicates a fault with the detonation sensor’s circuit. Because the ECU can’t detect knocking in this situation, it “errs to the side of caution” by enabling this safety mode.
Limp-Home Mode (Code 12/MAF Sensor)
The “limp-home” mode is enabled if the ECU cannot communicate with the MAF sensor, throwing code 12. Under normal operation, the MAF sensor meters incoming air and the ECU supplies an appropriate amount of fuel. If the ECU has a broken connection to the MAF sensor, it relies on a “backup map” which uses an air/fuel whose values reflect what the amount of incoming air should be given the current running condition (RPM, load, etc). The ECU also imposes a rev limiter around 2500 RPM when this mode is enabled, to prevent the engine from ingesting too much air (which could be dangerous to the engine without the correct amount of fuel).
Should the ECU receive a temperature reading of over 221°F, it enters an overheating safety mode. This mode enables the auxiliary cooling fan (on high speed for turbo models), switches to the low-octane fuel map (to protect against detonation, and decrease combustion temperature through additional fuel), and raises the idle speed to more quickly circulate coolant while increasing the cooling fan’s speed.
At this point, the stock temperature gauge will also begin to raise above the half-way mark.