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I've recently finished a cam/headers upgrade to my 02 Z06. I've had the car tuned and it's been running fine until recently. I've driven the car a few hundred miles after being tuned without any major problems but a few days ago my car started feeling like it was misfiring and was very difficult to drive. It had trouble staying on when stopped and when accelerating from a stop, the car was jolting very badly. The jolts continued until I got up to speed and stopped accelerating. When at a constant speed, the car still felt and sounded like it was misfiring. I had to pull over multiple times before finally making it home. The last time I pulled over, I turned the car off for about 10 minutes and it drove completely fine the rest of the way home. I'm thinking it's some sort of electical issue, mainly because my coolant temperature sensor was bouncing all over the place. I have since replaced the sensor but it didn't solve the problem. The indicator is maxed out even after a cold start. Anyone have an idea of where to start troubleshooting this? I added thermal insulation to all the wires around the headers and spark plug wires so I'm not sure if that's the issue. Before replacing the coolant temperature sensor, I found that the wire connector on the sensor was broken and the wires were just hanging and weren't connected to the sensor at all. I was hoping replacing the sensor would fix the problem since the wires now have a good connection, but that didn't work. I just want to be able to enjoy the car after all the hard work and time I've spent on it lately. Any thoughts are appreciated.
Are there any DTCs? I would check underneath for any wiring that may have fallen onto the headers, especially the O2 sensor wires. I’m sure others more knowledgeable will chime in.
When your ECT maxes out like that when cold the signal wire (yellow) is shorting to ground...first look at the wiring from the sensor to the wire bundle at the fuel rail where it joins...that 6-8 inch section runs underneath the alternator and then joins the wire bundle that runs along the left fuel rail...also look at the back of the fuel rail on that side and you’ll see what looks like a bracket sticking up...a lot of wiring issues happen there due to chaffing !!...a Forum member with almost the exact same issue is bringing his car by later today to have me look at it...I will let you know what we find...what happens when the temp pegs out like that the PCM will start shutting off injectors....4 to be exact to cool down the engine ...the car was only running on 4 cylinders !!!...this is where you should look as noted in the picture...I put a section of wire loom on mine !!....I would start looking here but it may be somewhere else in that harness. ALSO, check to see if you have a code stored...use can access your codes using the DIC...may be a P0117...that DTC will not illuminate the MIL and will show as a H...“history code” and if you can get the temp to max out continuously go and unplug the sensor connector...it should go to -38 degrees when unplugged...if not the wire is most certainly shorted to ground !!
Hey Buddy !!!...I can't think of anything other than the sensor wire shorting to ground somewhere in the harness either from the sensor to the wire bundle (pictured)
or at the harness bend at the rail...can you think of anywhere else ??????...I'm going to be going underneath mine a little later to check something out...I'll get out the tone generator and see where the rest of the harness goes till it finally gets to the PCM !!
The entire wire run on that side of the engine takes a beating sometimes depending on mods and maintenance completed. Yes, that bend around the bracket and connector at the sensor, Check for the 5 VDC Signal
Thanks for the great feedback! C5 those are some great notes on things to check. I’ve been out of town but will pull the engine codes and check that wire for shorts when I’m back. Hopefully it’s something that simple.
A Forum member came by today and his ECT would sometimes peg out at 260 while driving...sometimes even with a cold engine...we found chaffing on the fuel rail “stop bracket” but it didn’t look like it chaffed into the wiring...was difficult to get in there with my “surgical” tools but I may have to and really check...I put a piece of some plastic loom in that area for now...he took the car for a ride and he said so far so good..,really want to get in there and check the whole wire bundle with an inspection mirror !!
Does anyone have electrical schematics for this circuit to help me with troubleshooting? I measured 0 V and 0 ohms to ground on one of the wires and 5 V and an open load to ground on the other. This seems correct to me. My current DTCs are:
The P0118 ECT sensor high voltage and excessive time to closed loop fuel control is the one that deals with this issue. My fuel gauge shows maxed out too and I'm almost positive I don't have a full tank. It sounds like these two problems may be tied to this same code.
The DTC description makes it sound like the ETC circuit monitors the voltage applied to the ECT sensor and not current like I was thinking. If that's the case, I should have an open in the ground wire somewhere that's keeping the voltage high. This makes sense except for the fact that I can ohm out my wire from the sensor wire connector to ground, indicating a closed circuit and not an open. I'm thinking the problem could be due to something other than a bad wire from the sensor to ground.
Last edited by Twhittle14; Jul 17, 2019 at 01:41 PM.
OK so if you have a P0118 (with your symptoms I thought it would be a P0117) that’s a high voltage on the signal (yellow) wire...you probably have a broken wire on the brown wire between the sensor harness and the PCM ...using an ohmeter to check ground circuits is NOT the best test...loaded circuit testing is the way to go !!...(you can have 1 thin strand of wire remaining on that ground wire and with an ohmeter you will read continuity...for that strand of wire to carry current...FORGET ABOUT IT !!...take a 12 volt test light connected to battery positive and touch it to the brown wire pin at the harness...if ground is good the test light will light !!..,I use old headlight bulbs to load the grounds !!...with a scan tool you will see -38 degrees with sensor disconnected !!...that is also why you are staying in open loop for a long time...PCM is looking at ECT to determine when to go into closed loop !!...PCM is seeing -38...if you need the PCM pin outs for this circuit let me know !!..,reading your first sentence was a little confusing as far as what you were seeing. Was an OEM sensor installed or an aftermarket ??
I should have clarified how I was taking those readings. I measured the pins on the wire connector with it disconnected from the sensor and the car was on. I just wanted to verify I had 5V to the sensor. I'm suspicious of the sensor or wire connector now because the wires don't seem to have a problem. If the wires don't have a good connection to the sensor it would explain why I'm getting the error code as the circuit would be open and the 5V would never get pulled down. The sensor is aftermarket from the local auto parts store.
Fixed! It ended up being the wire connector to the sensor. I was able to test it by disconnecting the wire connector from the sensor, putting two jumper wires in the connector and connecting the other ends to my old sensor. Temperature gauge started reading correctly after that. I had to hold the jumper wires just right so apparently there is something faulty in the connector.
Electrical Issue?
