"left front tire locks up" - 2003 Ford Focus

Most likely a warped rotor and with new pads it has locked it's self up.

that is part time 4wd
and i bet has manual locks on both front axle ends.
how'd i know that.???? grin
first off PT 4wd is for ICE or offroad
SO if NO ICE roads handly (i cant see you drive)
then go off road, or gravel road, or not pavement.
then shift to 4wd.
the rear will have power, for sure.
so that means how to test the front end
i do so on jack stands
put the car up on left side
engine off.
lock the front left lock and right.
now turn the left tire by hand,, bingo you cant.

if you can and the axle behind it does not spin that means the left lock is bad.
if the left axle does turns and so does the right axle , that means th right lock is bad.
3 tire on ground rules. part time.
the front drive shaft will not turn, if it does the transfer case is not in 4H or 4L. if the transfer case is working the rear drive shaft can not turn, in this test. (cuz both tires are on the ground)
see manual locking hubs test here and failure modes.
http://www.fixkick.com/part-time-test.html

it could be a flex hose between the caliper and the steel line

Hopefully you still have you manual. I will tell you how to reset the HHR, I found it in my manual. Turn the key to on, press lock and unlock at the same time on your key fob. The horn will beep twice telling you that you are in program mode. The left front turn signal light will come on, press the valve core letting air out of the left front tire. The horn will beep when left front is programmed. Then the right front turn signal will come on, let air out till horn beeps. Then right rear, same procedure then left rear same procedure. When that is done horn will beep twice again saying tire program is complete. Turn key off, make sure you air all tires back up.

Tire pressure monitoring system. Start by checking your tire pressure and set to what the sticker on the drivers side door frame indicates. If this does not turn the light off you will have to re-learn the sensors to the vehicle. This is done by:
reset the tire pressure monitoring system, to do so, you need to get your key fob, and put your ignition key in the ignition, turn it to the accesories position, and simultaneously press the lock and unlock buttons on the key fob. hold them until the car honks the horn.

then take something to let out air in the tires, you need to start with the left front then go to the right front, then the right rear, then the left rear.

start at the left front, drop the pressure in the tire until the horn beeps, -usually takes 8 seconds or so. then repeat on the other tires in the order above.

After you finish with the final tire, the horn will honk again, then you know your done. usually honks 2 times.

and then you can turn the key off, and set your tire pressures.

This is a normal condition due to the fact that the diff is not a locking type differential.

On vehicles equipped with keyless entry, simultaneously press the keyless entry transmitters lock and unlock buttons until a double horn chirp sounds indicating the Learn Mode has been enabled. The left front turn signal will also be illuminated....Next

Increase/decrease the tire pressure for 8-10 seconds then wait for a horn chirp. The horn chirp may occur before or up to 30 seconds after the 8-10 second pressure increase/decrease time period has been reached. Once the horn chirp has sounded, the sensor information is learned and the turn signal in the next location to be learned will illuminate....Next

1. After the horn chirp has sounded and the right front turn signal is illuminated, repeat step 2 for the remaining 3 sensors in the following order:

1. Right front
2. Right rear
3. Left rear
4. When the left rear sensor has been learned and a double horn chirp has sounded, the learn process is complete and the RCDLR exits the learn mode.
5. Ignition OFF, adjust all tires to the recommended pressures. Refer to Vehicle Certification, Tire Placard, Anti-Theft, and Service Parts ID Label

try turn key on on do not start press lock and unlock at same time to put into learn mode for tps monitors adjust tire pressures left front right front right rear left rear in order.

Programming TPM Sensors
1. Turn the ignition to ON.
2. Press the key fob lock and unlock buttons simultaneously for several seconds. The horn will chirp when the TPM
programming mode is activated. Important: If the TPM programming mode cannot be entered, check if the DIM is
configured with the correct RPO codes.
3. Starting with the Left Front Tire
4. Install the J 41760 over the left front valve stem. Magnets from Radio Shack, P/N 64-1888 (at $2.99), will also work.
They're too small to go over the valve stem cap, but once you remove it they slip over the valve stem just fine
instead of the GM tool.
5. The horn will sound, indicating the Left Front TPM sensor is programmed. Important: If the horn does not sound after
15 seconds, remove then reinstall the TPM sensor programming tool or place the magnet alongside the valve stem.
6. When the horn sounds, proceed to program the next TPM sensor in the following order:
o Right Front Tire
o Right Rear Tire
o Left Rear Tire
7. After the Left Rear sensor is programmed, the horn will sound twice to indicate programming is complete.
Programming Cancellation
1. The programming mode will be canceled if any of the following conditions are met:
o The ignition is turned OFF.
o All four sensors have been programmed.
o The TPM system has been in the program mode for longer than 5 minutes and no sensors have been learned.
2. If more then one minute has passed before the next sensor is programmed, all previously stored codes are
erased from the receiver's memory.
after driving around for a few blocks, if the pressure does not match the tire pressure for each wheel, then the sensor is bad.