Here is where I'm at so far. I have a PO135 on the above mentioned vehicle. The fuse coming from the pcm power relay is good. After disconnecting 02 (key on) I have B+ going to the positive connector on the harness side 02 and less than 100 millivolts when voltage drop tested from the fuse to the B+ pin (heater supply voltage) on the 02 harness connector. So far so good, right? On the ground side (from 02 harness connector to PCM) I have 0.00 millivolts when voltage drop testing; and with the connector unplugged and DVOM connected to the positive terminal (key on) I have .15 volts registering on my meter. I know the signal is pulse width modulated, however, I should be getting at least 7 volts right? Second, when I switch my DVOM leads from B+ to ground and keep my other test lead on the heater control side of the circuit I am reading B+ voltage (with 02 disconnected I might add). To me, this would indicate a short to voltage, right? Third, when my oscilloscope is hooked up to the PCM harness connecter and the vehicle goes key on I briefly see B+ voltage followed by the PCM pulling the signal to ground, releasing, pulling to ground, and then after the second or third time it stays B+ voltage. When running, initially it does the same thing but after the third or fourth time it stays at ground. So my initial assumption is that I have a short to voltage in the harness along with a fried transistor inside the PCM (also of note, when scoping the bank 2 sensor 1 heater circuit the scope shows the exact same thing and both 02 pins are next to each other in the PCM). Could someone chime in on their thought/next steps/best practices moving forward?
The sensor is original ford?
confirm heater circuit resistance (2 and 1) between 3 and 30 ohms?
All other pins resistance greater than 10,000 ohms?
SWAG - an aftermarket part?
Conform I am on correct diagram
12V is RD/YE wire
control is RD/WH wire
* heater circuit resistance (2 and 1) between 3 and 30 ohms?
Trouble Code: P0135 (4.6L V8 VIN 6 Auto)
HO2S-11 Heater Circuit (Bank 1, Sensor 1)
Number of Trips to Set Code: 2
Trouble Code Conditions:
During testing the heated oxygen sensor (HO2S) heaters are checked for open and short circuits and excessive current draw. The test fails when the current draw exceeds a calibrated limit or an open or short circuit is detected.
•* Vacuum hose disconnected on exhaust gas recirculation (EGR) system module (ESM) applications
•* Short to VPWR in the harness or HO2S
•* Water in the harness connector
•* Open VPWR circuit
•* Open GND circuit
•* Low battery voltage
•* Corrosion or incorrect harness connections
•* Damaged HO2S heater
testing 93 to 94 IDK what you SHOULD see - should be open EXCEPT for the voltage sense ability?..
I am always see the issue before PCM (93, 94) the wiring to get the voltage to thise pins and the PCM not happy with it senses....
My trouble tree has us at current place with a replace PCM as next step I do not like to condemn PCM's I need time to reevaluate.
There are NO other codes?
Original issue P0135 (open Htr) and replacing sensor did not clear the issue?
A thought - Could the pin (93) - internal PCM be permanently grounded ?
A challenge -
Anal question - above you posted
"2,1 & 2,2 run through a different connector entirely (C101)." typo? C110on my dia?
PO 135 Freeze Frame: closed loop
ECT: 174.2 F
I feel we are down near the end of hope for PCM.
The monitors are setting I guess ?
Charging is good - Have you swapped o2 sensor?
When your scanner command s Htr can you see circuit activity?
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