1SlowHoe

iTrader: (28)

DTC P0178 Fuel Composition Sensor Circuit Low Voltage
I got this today. I've been getting the battery light on the dash at start up and had a code about low voltage last week. I read on here that this was common so I erased it and moved on. It hasn't come back but I got the one above yesterday and I'm still getting the battery light on the dash. Any ideas?

Got this from another site:
Yeah, it means it's going to cost you about $800 to fix it.

Your vehicle is capable of using fuel that is high in ethanol content, i.e. E85 fuel (85% ethanol and 15% petroleum based). In order to do so, it uses a sensor to determine how much alcohol is in the fuel. That's the Fuel Composition Sensor.

It's possible it could be a wiring problem, but every one I've seen that sets a FCS code has been the sensor itself, and it ain't cheap. The sensor is mounted on the frame on the right (passenger) side of the engine compartment. Look for a small box looking thing with two fuel lines running into it and an electrical connector.

Grumpy5.3

iTrader: (14)

I hate to say it but your guy you read from is right, 9 times out of 10 it is the sensor, and it is expensive!!!!! But you can check your batteryand make sure it is ok, and your charging system, you know normal stuff... then you should check and make sure you are getting proper voltage to your sensor, and good ground. but you will probably find that the sensor is bad.

1SlowHoe

iTrader: (28)

The price on the sensor has gone down to $320 and the fuel filter is $47 but I just replaced my filter about 2 weeks ago and it was only $35 at Advance Auto. I was wondering if this code will cause issues with driving? I dont use E-85 fuel because I don't think my Radix would like it. Is there a way to tell the PCM to ignore this sensor and/or remove the sensor all together? The truck still drives fine, no KR or anything and the fuel pressure is still good. Anything else it could affect? The spark is staying where it should as well. Under 20-21* at WOT

Nick™

iTrader: (2)

all powertrain codes can be removed with most tuning programs, how is your truck tuned? if not custom then try to find someone in your area with HP Tuners for you model and have them turn it off, only takes a couple minutes if they know what they are doing.

dewmanshu

iTrader: (4)

couple of secs actually...the time is in plugging up to the pc downloading and uploading.

1SlowHoe

iTrader: (28)

I have a Predator to erase the code with but, I'm more concerned as to why it was set. Could it be just a voltage issue which triggered my other code? They both seem to be related to low voltage inputs and I'm still getting the battery flash on the dash at start-up. Is there a way to check the Alt for proper output without taking it off and to Autozone?

1SlowHoe

iTrader: (28)

But just to make sure I understand...you are saying that HPT or EFI Live should be able to tell the PCM to ignore inputs from that specific sensor so it wont trip the code again? I don't care if that sensor works or not because I'm not ever going to run E-85 fuels. Hell, I don't think I could if I had to at this point.

thunder550

iTrader: (70)

HPT has a screen where you can take a code and choose how the PCM responds to it. See attachment...you can change the response to any DTC code.

Nick™

iTrader: (2)

yep, as stated above, you can use the aforementioned programs to make it either not set the ses light, but still take note of the problem or you can ignore the sensor all together... sounds like in your senerio this wouldn't hurt a thing.

As for the battery light:
any automotive shop / part store can test your alternator and battery while on the car - just bring it in and get it checked out.
are you still using the original alternator from your truck (or a direct replacement)? I know you have the motor swap and all, if you put a different alternator (lower amp) it could be causing this issue also... and it wouldn't test bad either (works, just not what the truck is looking for)

1SlowHoe

iTrader: (28)

I erased the SES/DTC code. If it resets I'll have it tuned out. The alt is the stock one from the 5.3. It has 70K miles on it so I guess it could be going out. I will get it checked next week. The battery always turns the truck over strong so I think it is charging fine and the volt meter on the cluster is always above 14 but I think it could be off just as the speedo and tach are.

Key on

Starting (while turning the key)

Running

Dash light (goes out after the engine is running)