Sunday, November 12, 2017

Intermittent Cruise Control

We've had a worsening problem with intermittent cruise control operation on our late 2003 E450. The cruise control operated as it should for many years, but then we began to experience periods when it wouldn't activate. This got steadily worse until on our last trip it hardly worked at all, despite pushing all the steering wheel controls repeatedly and in various orders and checking other things.

A post on this site and a number of posts elsewhere suggest that the most likely culprit in this situation is the cruise control deactivation pressure switch on the bottom of the brake master cylinder. This switch provides redundancy to the mechanical switch on the brake pedal, creating two ways that the cruise control is deactivated when the brakes are activated.

Similar switches have been the subject of recalls on various Ford vehicles due to the slight risk of fire should they leak, resulting in brake fluid reaching the electrical contacts and igniting. That can apparently happen even when the vehicle is parked. But our E450 was not part of that recall, having been built in May 2003 after the problem was presumably solved.

That doesn't mean that this switch can't fail though, and when it does it fails so as to leave the cruise control deactivated, which makes sense. In our case and many others, this seems to happen slowly with the switch working sometimes and not others.

I ordered a new switch here:

New Motorcraft SW-6350 Cruise Control Cutout Switch 1L1Z-9F924-AA * P184 * |...

[If the eBay link above goes dead, Google for Motorcraft SW-6360]

That is actually a kit for replacing the switch "in kind" on newer vehicles like ours and also apparently upgrading the switch on older vehicles that used a different one. Thus it includes a short wiring harness to adapt the old electrical connection to the new switch. It's actually useful to have that even if you don't need it, as it allows you to clearly understand how the connector detaches from and attaches to the switch, always an annoying step when working with automotive electrical connectors. Sometimes figuring out how they work is the hardest part of a job like this.

To gain access to the switch I worked from the fender on the driver's side of the engine bay. I removed the three bolts that hold the round plastic coolant reservoir and moved it out of the way. No need to detach its plumbing. Leave the cap on and no coolant will spill. Then I moved some other cables out of the way and held them aside temporarily with zip ties.

I then placed a towel down under the switch to catch the few drops of brake fluid that will result from this and to catch any dropped tools or parts and keep them from descending into the nether regions of the engine bay.

Then I removed the electrical connector from the old switch. Use the wiring harness that came with the new switch to figure out how to do that. Then I removed the switch itself. Both my old and new switches require a 7/8" wrench. Older switches might be different. I just used a small crescent wrench to loosen the switch and then removed it the rest of the way by hand. The shorter the wrench the better as space is tight.

Before you fully remove the switch note that it is tapped into the brake master cylinder at an angle. You will need to install the new switch at the same angle. Failure to notice this could result in a lot of frustration when trying to thread the new switch into its receptacle. You'll get a few drops of brake fluid coming out with the old switch. But provided you leave the cap on the master cylinder reservoir you won't get any ongoing dripping from the hole into which the switch is threaded.

I hand tightened the new switch and then snugged it up tight with the crescent wrench. Don't over tighten. I then reconnected the wiring and went for a drive and the cruise control worked flawlessly. I'll be keeping an eye on the new switch for awhile to be sure it isn't leaking brake fluid.

It's very gratifying to fix something like this, that has been an ongoing and puzzling annoyance, for the grand sum of $18 and about 15 minutes of time. As opposed to going to a mechanic who might or might not know about this problem and who could spend hours going through all the steps for diagnosing cruise control problems and/or replacing several much more expensive parts before finding the culprit and fixing it. A process that would be made more difficult if the cruise control happened to be working while it was in for diagnosis.

If your cruise control is intermittent or not working I suggest giving this a try as a first step.
Terry Burnes - October 2017

A slightly helpful YouTube.