What causes Ford code 174?

The HO2S switches too slowly because the sensor is aged or contaminated. An intake leak or a rich mixture slows the switch. Fuel pressure outside spec delays the switch. A clogged or leaking injector skews the mixture and slows the switch. The HO2S wiring adds resistance that slows the signal.

How do I fix Ford code 174?

Check for an intake leak. Check fuel pressure against spec. Check the injectors for a clogged or a leaking one. Test the HO2S switch time 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 the HO2S switches within time.

Ford 174 HO2S switching time is slow

Q: What does Ford code 174 mean?

Ford code 174. HO2S switching time is slow.

Make: Ford (1981-1995)
Category: Powertrain - Fuel/Air Metering
Severity: Check Engine Light

How to read it

Code 174 reads as 1 flash, pause, 7 flashes, pause, 4 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 174 mean?

HO2S switching time is slow

Common causes of 174

The HO2S switches too slowly because the sensor is aged or contaminated.
An intake leak or a rich mixture slows the switch.
Fuel pressure outside spec delays the switch.
A clogged or leaking injector skews the mixture and slows the switch.
The HO2S wiring adds resistance that slows the signal.

How to fix 174

Check for an intake leak.
Check fuel pressure against spec.
Check the injectors for a clogged or a leaking one.
Test the HO2S switch time 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 the HO2S switches within time.

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. The three-digit 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 trouble codes, Contour, Escort, Mustang, Probe, Taurus and Tempo 1992-1995 (code, description, 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 a probable cause column.
http://web.archive.org/web/20160501223306id_/http://www.troublecodes.net:80/ford/contour-escort-mustang-probe-taurus-tempo-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 174. Include your vehicle, the issue and a source if you have one.