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Discussion Starter #1
Can someone help?? 2004 SVT check engine light came on code P0135 front sensor bad replaced the front before cat. sensor. reset the check engine light came right back on. Code is the same now both sensors show bad. Found fuse #18 blown replaced and it blew again. Can someone help as to where I need to look for shorted wires. I have checked the rear and dont see any rubbed wires[?|]
 

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BACON?
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You should be looking that the wiring for the front O2S because the code if for sensor one bank one. "Code is the same now both o2s show bad" If the code is the same then how is the rear o2s "showing bad?" Just keep looking at the front o2s wiring.

Do you own a DMM (digital multi meter)? That can really simplify the diagnostics. figure out which wires are for the heater circuit. disconnect the wiring from the ECU and the o2S. then measure the resistance between the two wires, should read open. then read the resistance between 1 wire and a ground, again should read open. and repeat on the last wire, it should read open again. and reading of low resisance indicates there is a short to ground. the next step is to find the short. You can look at all the places where the wires might rub, or find any connectors in between the ECU and the sensor. retesting the resistance at each connector will help to narrow down the possible locations of the open. If you are really pulling your hair out you can just go a head and replace the wires.

Also could try disconnecting both sensors and seeing if the fuse blows again. Its likely it will because the sensor was just replaced.

And for future reference a DTC code can NEVER tell you a sensor is "bad". All it can do is point you in the general direction of the issue. Its up to you to diagnose if its indeed the sensor, the wiring or the module itself. P0135 reads Oxygen Sensor Heater Circuit Malfunction (Bank 1, Sensor 1). Just some tips for future diagnostics.
 

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DTC P0606
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Some extra info in addition to alex's:
It's a pretty simple circuit. From the engine fuse box, power goes via fuse 18 to the front and rear O2 sensor: The front O2 sensor power via a green/yellow wire; the rear via green/blue. The green/blue is spliced into the green/ yellow wire further up in the harness so that both sensors share the same power source and fuse.

Power the front and rear sensors separately (unplug one), as suggested, and see which one is blowing the circuit fuse to isolate the problem to either front or rear sensor now that you know that they both run off the same power source. It's unlikely, though not impossible, that the harness has a chafed wire or dead short in it if you've inspected it visually and not found any obvious problems. In that case, I'd check the sensor electrical connectors themselves for bent pins, moisture, corrosion or crud build up.
 

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Discussion Starter #4
Thanks for the info. I do have a tester and will try that next. As for the connections I saw no corrosion or bent pins but will look closer. [scratch]
 

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Discussion Starter #6
Oxygen sensor

I got to the testing of the sensors and unplugged both and put in a fuse turned the key and it didnt blow the fuse. Plugged the front in and didnt blow. then rear sensor blew the fuse. Removed it and saw a small dent on the top of the sensor which probably shorted it inside. Could a small pothole cause this and if so is there any way to protect it other than not hitting holes. Also what is the aftermarket part number for the after cat. sensor. The parts stores say it is the same as the front. The look different. The number on the sensor is XR3F-9G444-B1A
 

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Discussion Starter #7
oxygen sensor

Finally got the proper sensor put in after cat. Everything is working good no cel.[burnout] Thanks for all the help.
 

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fuse 18

Mine has been blowing, does fuse18 only run the O2 sensors? Would there be anything else connected?
 
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