Limp mode troubleshooting

[Steve Bassen]

Background info: 2004 F-150, 60k, 5.4L 3v, intake/exhaust and Troyer tune So I was going to work, tonight, and was about a mile away, when I ended up doing a nice WOT pull to get around a slow fuel tanker truck. Around the top of second gear, the truck bucks and goes into limp mode (amber wrench light on the dash). By then I'm pretty much at work, so I cruise in to the parking lot and shut it off (it's running in limp mode during all of this). I hook up my XCal2 and check for codes; no DTC's found. I start it back up, and it's back out of limp mode, but the CLE is illuminated, despite no codes. My first thought is the TPS sensor is on its way out, although that usually includes DTC codes, unless it wasn't on long enough while it was in limp mode (less than a minute). Thoughts?

[Steve Bassen]

Well I just went out and tried pulling codes again, and this time was successful. 6 codes, woo hoo!

P0010 Intake Camshaft Position Actuator Circuit/Open (Bank 1)
P0020 Intake Camshaft Position Actuator Circuit/Open (Bank 2)
P0135 O2 Heater Circuit (Bank 1, Sensor 1)
P0155 O2 Heater Circuit (Bank 2, Sensor 1)
P0443 Evaporative Emission System Purge Control Valve Circuit
P0446 Evaporative Emission System Vent Control Circuit

Judging by the sheer number and randomness, I'm guessing this was a glitch of some sort. Will clear them and see if it returns.

[sburn]

Originally Posted by Steve Bassen

Well I just went out and tried pulling codes again, and this time was successful. 6 codes, woo hoo!

P0010 Intake Camshaft Position Actuator Circuit/Open (Bank 1)
P0020 Intake Camshaft Position Actuator Circuit/Open (Bank 2)
P0135 O2 Heater Circuit (Bank 1, Sensor 1)
P0155 O2 Heater Circuit (Bank 2, Sensor 1)
P0443 Evaporative Emission System Purge Control Valve Circuit
P0446 Evaporative Emission System Vent Control Circuit

Judging by the sheer number and randomness, I'm guessing this was a glitch of some sort. Will clear them and see if it returns.

Except for the EVAP Vent, all of the above share the same electrical circuit. Fuse F32 in my 2007 manual, but I expect your year (unless Heritage) should be the same. Loose fuse, maybe? Loose connector on the fusebox?

[Steve Bassen]

Good call... I'll give that a check.

[Steve Bassen]

Right on the money. Fuse 32 was blown; replaced it and drove it 5 feet before it blew again... ugh. Looks like I'll have to track down what's blowing it.

[sburn]

Originally Posted by Steve Bassen

Right on the money. Fuse 32 was blown; replaced it and drove it 5 feet before it blew again... ugh. Looks like I'll have to track down what's blowing it.

An O2 heater shorted to ground internally would be be my next educated guess.

[ManualF150]

Check the wires on the o2 sensors... or else the heater decided to die, then you need to get a new o2 sensor.

[Steve Bassen]

Well this is weird...

So I was measuring the circuit resistance from the fuse box. Naturally, it was reading a short to ground somewhere. I started unplugging stuff, starting with the O2's, one by one. I get to the driver's side post-cat O2 and it magically goes to 13 ohms overall, once it's unplugged. Just for grins, I plug that one back in. Still 13 ohms. So I hook everything back up, throw a fuse in, and clear the codes. Truck's running fine. So somehow, the O2 sensor is no longer grounding out the entire circuit, after being replugged in. I'm going to order a replacement, regardless, before I get any confidence back with this thing....

[Fireman1291]

So what happened?

Im having the SAME problem ver batem....

[Steve Bassen]

Not sure what happened... after I plugged it back in, it was fine. I did replace the o2 sensor, just in case, and it's been fine since. Just probe the fuse block for the fuse that keeps blowing and start unplugging stuff (MAF, cam position sensors, O2's) until it stops reading a short.