What causes Ford code 45?

Secondary air was delivered upstream during the self test when it should not have been. The AIR solenoid stayed open and sent air upstream. A vacuum hose to the AIR system is damaged or connected wrong. The ECM could not switch the AIR flow.

How do I fix Ford code 45?

Check the AIR solenoid and confirm it closes during the self test. Check the vacuum hoses to the AIR system for damage or a wrong connection. Check the AIR passages for a blockage that holds air upstream. Test the AIR solenoid and replace it only if it fails its own test. Test the ECM last, only after every circuit test has passed. Clear the code, then retest to confirm air does not go upstream during the self test.

Ford 45 Secondary air upstream during self test

Q: What does Ford code 45 mean?

Ford code 45. Secondary air upstream during self test.

Make: Ford (1981-1995)
Category: Powertrain - Auxiliary Emissions Controls
Severity: Check Engine Light

How to read it

Code 45 reads as 4 flashes, pause, 5 flashes on the check-engine light. Jumper the self-test input to signal return at the test connector, then run the key on engine off self test and the running self test, counting the check-engine flashes each time.

New to flash codes? The How to Read Ford EEC-IV Self-Test Codes walks through the test and what the numbers mean. The general OBD-I guide covers the rest.

What does Ford code 45 mean?

Secondary air upstream during self test

Common causes of 45

Secondary air was delivered upstream during the self test when it should not have been.
The AIR solenoid stayed open and sent air upstream.
A vacuum hose to the AIR system is damaged or connected wrong.
The ECM could not switch the AIR flow.

How to fix 45

Check the AIR solenoid and confirm it closes during the self test.
Check the vacuum hoses to the AIR system for damage or a wrong connection.
Check the AIR passages for a blockage that holds air upstream.
Test the AIR solenoid and replace it only if it fails its own test.
Test the ECM last, only after every circuit test has passed.
Clear the code, then retest to confirm air does not go upstream during the self test.

Source

Source review recorded

Sources and review

Review: checked against the recorded source material.

EEC-IV Ford trouble code table (MIL, description, type)
archived reference page (troublecodes.net via Wayback Machine)
Supports: code identity and meaning
Fetched directly. Code row matches the description used in the data file.
https://web.archive.org/web/20030720231430id_/http://www.troublecodes.net:80/Ford/eec-iv.shtml
Ford EEC-IV trouble codes, Crown Victoria, Mustang, Taurus, Thunderbird 1992-1995 (code, fault location, probable cause)
archived reference page (troublecodes.net via Wayback Machine)
Supports: code identity and probable causes
Independent table on the same archive site with matching code identity and additional probable causes.
https://web.archive.org/web/20160502051413id_/http://www.troublecodes.net:80/ford/crown-victoria-mustang-cobralxgt-taurus-thunderbird-1992-1995/
Ford EEC-IV trouble code table: code, fault location, probable cause (Crown Victoria, Mustang, Taurus, Thunderbird 1992-1995)
reference page (troublecodes.net)
Supports: per-code probable causes used for the page cause list and test order
Fetched 2026-09-30. The probable cause column is what the page lists, in source order, with the test order built from it.
https://www.troublecodes.net/ford/crown-victoria-mustang-cobralxgt-taurus-thunderbird-1992-1995/

Last updated 2026-10-10.

Report a correction for 45. Include your vehicle, the issue and a source if you have one.