The Dreaded Yellow Wrench.

UPDATE : My "fix" described below was not successful in avoiding the yellow wrench; to really fix it you need to replace the actuator. But the steps are as described.


I've been getting the yellow wrench light sporadically for the past few months. Several times I was able to pull over, turn the car off and then back on, and it didn't return (during that trip) so I assumed it wasn't urgent. I did call the local Ford dealer and they suggested I bring it in as soon as possible to get checked out; "It's likely just the blend door actuator but you never know what could go wrong with those hybrid systems." He wasn't able to give me a verbal estimate of what it would cost to diagnose (I didn't like this), and acted concerned when I told him that it was not under warranty. I figured (as he did) that it was probably an issue with the actuator motor for the rear battery AC vents. I noticed that the light was most prone to come on when I was doing a lot of low speed driving in full electric mode, such as in stop-and-go traffic.

The hybrid Escape has a battery pack in the rear of the car that gets warm with use. To keep it cool there is a special AC system fitted in the left rear of the vehicle. Just like the main AC system, there are two modes: "recirculate" or "fresh-air". Most of the time the system recirculates the air inside the system, but occasionally it wants to open the vent and get some new air in from outside. That's where the blend door actuator motor comes in.

It's pretty easy to pull off the rear trim to get to the battery AC system, but getting the motor itself off is a real pain. There are three 5.5mm screws holding it in, and one of them is nearly impossible to remove. You can see two of the screws in the picture here; when reinstalling the motor I only put in the easy two screws, in case I ever need to get in there again.

Here's a diagram showing all the little bits you'll need to remove to get access to the motor. It's actually not as hard as it might look.

After removing the motor I decided to pop it open. It's actually pretty simple inside: a DC motor, some reduction gears, and some carbon tracks with a wiper used as a potentiometer or variable resistor so the controller can tell where the motor is (open/closed/in motion/etc). I didn't see anything obviously wrong with it. I was particularly interested in the two small clips that the motor lugs press into to allow easy assembly. However, I noticed that when the motor was in place in these clips it wiggled slightly and it looked to me like it might lose contact with the clips. Just to be sure I installed the motor and soldered the lugs to the clips. I also wiped off the wiper tracks with a Q-tip and some rubbing alcohol.

It snapped back together easily and I reinstalled it (minus the third screw). You'll notice on the outside of the motor there is an arrow pointing to the shaft, and there is a flat spot on the shaft that lines up with this arrow. When you reinstall the motor the doors will not be shut, nor will they be open all the way. They will be in the middle of their travel. Usually the doors are shut. When you turn the car back on it will reset the door to the right position.

I haven't seen the wrench light since (one month so far) but I'll let you know if it ever comes back.

Finally, here's the text from the related Ford TSB (technical service bulletin). The last step mentions recalibrating the battery module, which I am not able to do, but it is not required.


TSB
07-25-12
WRENCH LIGHT ON - DTC B1239
Publication Date: December 7, 2007
FORD:
2005-2008 Escape Hybrid
MERCURY:
2006-2008 Mariner Hybrid
ISSUE:

Some 2005-2008 Escape Hybrid and 2006-2008 Mariner Hybrid vehicles may exhibit a wrench light on with DTC B1239. This may or may not be accompanied by driveability symptoms including reduced power.
ACTION:

Follow the Service Procedure steps to correct the condition.
SERVICE PROCEDURE

Replace the Traction Battery Auxiliary Mode Door Actuator.
Remove the left hand D-pillar trim panel. Refer to Workshop Manual (WSM), Section 501-05.
Remove the four (4) battery airflow duct screws, the one (1) pin-type retainer and remove the battery airflow duct assembly.
Remove the two (2) auxiliary climate control fresh air inlet duct nuts and remove the duct.
NOTE: THE D-PILLAR BRACKET WILL REMAIN IN PLACE.
Remove two (2) upper climate control housing bolts and two (2) lower climate control housing nuts.
Position the climate control housing to gain access to the auxiliary mode door actuator.
Disconnect the auxiliary mode door actuator electrical connector.
Remove the auxiliary airflow mode door actuator screws.
Remove and replace the auxiliary airflow mode door actuator. Inspect actuator for free movement from any obstructions including the wiring harness.
Install the auxiliary airflow mode door actuator screws. Tighten to 18 lb-in (2 N-m).
NOTE: THE AUXILIARY CLIMATE CONTROL HOUSING MUST BE INSTALLED BEHIND THE LOWER PORTION OF THE D-PILLAR BRACKET. WHEN INSTALLED CORRECTLY, THE AUXILIARY CLIMATE CONTROL HOUSING BOLT WILL GO THROUGH THE D-PILLAR BRACKET FIRST, THEN THROUGH THE HOUSING MOUNTING LOCATION.
Connect auxiliary mode door actuator electrical connector and position back the climate control housing.
Install two (2) upper climate control housing bolts. Tighten to 62 lb-in (7 N-m).
Install two (2) lower climate control housing nuts. Tighten to 53 lb-in (6 N-m).
Install the auxiliary climate control fresh air inlet duct and tighten nuts to 62 lb-in (7 N-m).
Install the battery airflow duct assembly, pne (1) pin-type retainer and the four (4) screws. Tighten to 18 lb-in (2 N-m).
Install the left hand D-pillar trim panel. Refer to WSM, Section 501-05.
Reprogram the Traction Battery Control Module (TBCM) to the latest calibration using IDS release B52.5 and higher with Patch 7. This new calibration is not included in the VCM 2007.11 DVD. Calibration files may also be obtained at www.motorcraft.com.

PART NUMBER PART NAME
8L8Z-19E616-E Auxiliary Mode Door Actuator

33.54 MPG

433.6 mi, 12.927 gal @ $3.659 = 33.54 MPG

71,097 total miles. Chevron on Hamilton and Bascom.

Just before this fill-up I checked the tire pressure and put it back where I like it (40 PSI). I'm expecting the next tank to be much improved over the past few months, but this one was already gone when I re-inflated.

Inflated tires to 40 PSI.

Well I may have been wrong about the "winter gas mixture" causing my mileage to fall. I've noticed that since mid October it's been lower than usual, and have been slowly debugging all the possible causes. Today I finally got around to checking the tire pressure, and they were all sitting nicely at 35-36 PSI. I suppose I can thank my local dealer for that, although the last oil change was in September and I had pretty good mileage all through October.

Anyway, I put them all back up to 40 PSI (cold). I've got about 60 miles left on this tank, so we'll see if the next one improves.

Also, always remember to check the air in your spare tire when inflating the others. I've found the spare tire to be nearly flat in many vehicles, both mine and family member's. A deflated spare tire is useless; you might as well just leave it at home and save yourself the weight and space. In this case mine was fine because I'd checked it previously less than a year ago.

35.07 MPG

478.4 mi, 13.643 gal @ $3.559 = 35.07 MPG

70,663 total miles. Chevron on California Circle.

Improved, but still not stellar mileage. At least the price of gas is going down (temporarily I'm sure). I did pull off the roof rack crossbars right at the start of this tank, but it doesn't seem like that's had a huge effect. My MPG has been down about 5-10% since my last fill-up in October.

33.63 MPG

449.4 mi, 13.364 gal @ $3.659 = 33.63 MPG

70,185 total miles. Chevron on California Circle.

Ouch, this is the worse mileage I've had in a while. Following October I had a pretty steep fall off. I guess I should check the tire pressure and see if removing the roof rack crossbars pulls it back up. My guess though is that this is the effect of the winter gas mixture.