P2450: EVAP switching valve produces too little pressure change

P2450 detects an insufficient pressure response when the leak-detection switching valve changes position in the reviewed GM fuel-tank-zone-module system. Although the generic title includes stuck open, the source describes detecting a stuck valve from its effect on vacuum without proving one universal final position.

The reference measurement makes the comparison

The system first measures vacuum through a 0.020-inch reference orifice. With the pump commanded on, the switching valve then moves from vent to pump position. A working vented system should show a substantial vacuum drop followed by a slower increase.

If the change from the first reference vacuum is less than 400 Pa after five seconds, the monitor fails. This is a relative pressure-response test; an isolated absolute pressure reading does not reproduce it. A detected failure ends that EVAP diagnostic sequence.

This is a scheduled off-state test

The documented wake-up windows occur hours after propulsion becomes inactive: 4.3–5.8, 6.0–8.1 or 8.2–11.0 hours. Other conditions include fuel level between 10% and 90%, barometric pressure between 70 and 110 kPa, and specified temperature limits.

Key-up or an active service-bay test aborts the normal sequence. Consequently, absence of recurrence during a short engine-running inspection is not evidence that this monitor completed.

Verification should preserve the reference vacuum, transition response and eligible test status. Follow the applicable EVAP procedure to distinguish a valve problem from pressure-measurement or system conditions. The source lists Type B, two-trip behavior, without a mandatory valve replacement.

Source and applicability

Confirm the reporting module, system and calibration before applying these diagnostic limits. GM diagnostic table, PDF page 652.