07 v6 4.0 wiring issue .In desperate need of help.

List of Codes & What They Have in Common
P0135, P0155, P0141, P0161 – All four O2 heater circuit faults (both banks, both upstream and downstream).
P0403 – EGR solenoid circuit fault.
All of these are low-current solenoid or heater circuits that share power and ground feeds from the PCM.

Check Fuses (FIRST!)
On the 2005–2009 V6 Mustang, O2 heater power and EGR solenoid power are fed by:
Fuse 41 (15A) – Engine Control
Fuse 47 (20A) – PCM Power Relay
Verify both fuses are not blown and have battery voltage with key ON.
Also check Fuse 43 (O2 heater circuit, 15A) just to be safe.

Verify Power to the Circuits
Back-probe any upstream O2 sensor connector with key ON:
One of the pins should have battery voltage (usually Red/White wire).
If you do NOT see battery voltage, trace back to the PCM power relay circuit.

Check PCM Grounds
The PCM and all those sensors rely on G103 ground (on left front of engine block near A/C compressor bracket).
Remove, clean, and reinstall that ground.
Look for broken wires or corroded eyelets.

Check Continuity on Heater Grounds
The O2 heater ground wires (usually White or Gray) go straight to the PCM for control.
With key OFF, measure resistance from sensor heater ground pin to PCM connector pin:
Bank 1 Sensor 1 – PCM pin 93 (example)
Bank 2 Sensor 1 – PCM pin 94
Exact pins may vary – a pinout is helpful.
You should read less than 5 ohms.

Inspect Harness
Pay special attention to:
Harness running down back of engine (can melt on exhaust)
Harness over transmission bellhousing
Connector C175B (big square PCM connector) – look for bent pins or water intrusion

VSS Signal Showing 72 at 40
This could be unrelated, but also points to a 5V reference or ground issue.
Check the 5V reference at MAP or TPS with key ON – should be 4.8 to 5.1 V steady.
If it’s low, PCM may be pulling down because of a short in another sensor (unplug sensors one by one and see if 5V recovers).

Last Resort: PCM
Only after verifying power, ground, and continuity should you suspect PCM failure.
PCM failures are rare – most “bad PCM” cases turn out to be power/ground problems.