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Jimm

Jimm 11/22/2014

2005 Ford F-150 XLT 8 Cyl 5.40L

Engine

What can cause intermittent S32 fuse (20 amp) position open circuit failures?

Wife's F-150 (148k miles and regularly maintained) will intermittently open the fuse position S32 (20 amp) with multiple or numerous OBD codes and limp mode / reduced power resulting; O2 sensors, valve cam timing, etc and all different systems - in some cases up to 33 separate fault codes stored at one time.
My first thought is wiring harness and connectors common to the S32 fuse power wiring. What are some other possibilities to trace an intermittent S32 fuse open condition?

3 Answers


HouseCallAuto

HouseCallAuto 11/23/2014

Hi Jim. The reference to "S32" is throwing me some. All wiring diagrams I look at use an "F" such as fuse F32 which protects various circuits such as O2 sensor and Variable Valve timing components and many other components. can you clarify where this fuse is located to assist me with advice for you? This fuse is in the cabin or in the engine compartment and where does it reference the "S" you mention?

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Jimm

Jimm 11/23/2014

HCA thanks for the reply and thank you in advance for your assistance. The 'S' designation should be corrected to simply fuse #32.
This fuse is located right next to the Relay #201 (half ISO relay for the DRL disable) for the Trailer tow park lamps, in the fuse panel.

The fuse 32 reference is from the vehicle owners manual (page 227) description and diagram of the relays and fuse positions (page 225) within the fuse/relay distribution box - passenger side lower kick panel.

The 20 amp fuse will open intermittently and sporadically - in some cases after two weeks or more of vehicle operation time - to trigger: CEL, limp mode / reduced power and a variety of fault codes, for these affected systems and components;
Vapor management valve (VMV), A/C clutch relay, Canister vent, Heated exhaust gas oxygen sensors (HEGO) sensors #11 and #21, Mass air flow sensor (MAF), and the VCT (variable cam timing).

My thought process for beginning diagnosis is to examine common wire feed to and from the fuse panel / distribution box for the fuse #32.
With the intermittent frequency of the occurrence , the idea would be to examine for wire chafing, shorts and opens along the wire path - maybe individual wire insulation damage through to the copper conductor.
Other thoughts, tips or ideas?

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Jimm

HouseCallAuto 11/23/2014

The most common cause of Fuse 32 opening is caused by wiring melting on the exhaust manifolds as this fuse protects the heater corcuit of all 4 O2 sensors. Among other things that the fuse also protects.
This wire provides the supply voltage to the following components;
a) Evaporative Emission (EVAP) Canister Purge Valve
b) EVAP Canister Vent Solenoid
c) A/C Clutch Relay
d) O2 heaters in all 4 O2 sensors
e) both VCT solenoids
f) Mass Airflow (MAF) sensor
g) Charge Motion Control Valve

Jimm

Jimm 12/24/2014

Located and repaired the issue; burned / damaged transmission cable at the rear side of the exhaust manifold on the drivers side. Found a small burned spot on the cable that intermittently would touch and ground to blow that one 20 amp fuse in the #32 position.

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