Low Voltage.. New ECU?
09-07-2020, 02:40 AM
#1
Low Voltage.. New ECU?
MY03, 80k miles
Hopefully i can make this brief and to the point. Basically, I've been trying to diagnose a low voltage issue however now i am thinking i may have an ECU problem.
- recently had the head gasket replaced
- car runs fine above 2000rpm
- at idle the car sometimes will lose EPS, however, I just turn the car off/on and all will be normal again.
- checked voltage (+)/(-) battery. ~12.4V (engine on no accessories) and ~13.8V (engine on w/ all accessories). The voltage would drop sometimes to ~10V for a few seconds.
- replaced with new alternator (new from autozone, not refurbished). the voltage doesn't drop to 10V anymore but i am still getting ~13.8V with all accessories on. Still seems low.
- (+)battery to alternator housing also shows ~13.8V.
- I also replaced the EPS control module off an 01. Haven't lost EPS anymore, however steering feels more firm than i remember.
- Today at idle, the battery and park light flashed for second, however driving was normal after that. I figured the voltage dropped but not long enough to shut any systems off.
- Connected bluetooth OBDII and Torque lite to check voltage.. voltage from OBD adapter confirmed my readings, however, Voltage from control module showed "no data".
- No check engine light however, OBDII had a stored fault of P0325 (knock sensor).
- always starts up fine and voltage shows more than 12V so i don't think its the battery. (battery is about 5yrs old)
Based on these seemingly quirky symptoms i'm starting to think my ECU is the problem.
What do you all think? Do i have any ECU problem or is this all somehow due to a corroded wire somewhere?
Hopefully i can make this brief and to the point. Basically, I've been trying to diagnose a low voltage issue however now i am thinking i may have an ECU problem.
- recently had the head gasket replaced
- car runs fine above 2000rpm
- at idle the car sometimes will lose EPS, however, I just turn the car off/on and all will be normal again.
- checked voltage (+)/(-) battery. ~12.4V (engine on no accessories) and ~13.8V (engine on w/ all accessories). The voltage would drop sometimes to ~10V for a few seconds.
- replaced with new alternator (new from autozone, not refurbished). the voltage doesn't drop to 10V anymore but i am still getting ~13.8V with all accessories on. Still seems low.
- (+)battery to alternator housing also shows ~13.8V.
- I also replaced the EPS control module off an 01. Haven't lost EPS anymore, however steering feels more firm than i remember.
- Today at idle, the battery and park light flashed for second, however driving was normal after that. I figured the voltage dropped but not long enough to shut any systems off.
- Connected bluetooth OBDII and Torque lite to check voltage.. voltage from OBD adapter confirmed my readings, however, Voltage from control module showed "no data".
- No check engine light however, OBDII had a stored fault of P0325 (knock sensor).
- always starts up fine and voltage shows more than 12V so i don't think its the battery. (battery is about 5yrs old)
Based on these seemingly quirky symptoms i'm starting to think my ECU is the problem.
What do you all think? Do i have any ECU problem or is this all somehow due to a corroded wire somewhere?
09-07-2020, 11:33 AM
#3
I'm just about ready to lift the car to check grounding points.
I wanted to check the actual output of the alternator. So I checked the voltage between the (+) on the alternator and the alternator housing and I got 14.0V. so it seems like I'm loosing about 0.2V between the alternator and battery. Doesn't seem unreasonable to me but does this mean I got a bad alternator?
I wanted to check the actual output of the alternator. So I checked the voltage between the (+) on the alternator and the alternator housing and I got 14.0V. so it seems like I'm loosing about 0.2V between the alternator and battery. Doesn't seem unreasonable to me but does this mean I got a bad alternator?
09-09-2020, 10:21 AM
#4
Don't forget these cars have Electric load detector what Ecu uses to control charging voltage. https://www.civicforums.com/forums/3...-detector.html
13,8V charging voltage is fine according to S2000 service manual, so alternator is working correctly.
0,2V voltage drop could be bad connection on power wires or ground wires.
13,8V charging voltage is fine according to S2000 service manual, so alternator is working correctly.
0,2V voltage drop could be bad connection on power wires or ground wires.
09-09-2020, 12:09 PM
#5
As a reference item, ECU failure is actually pretty rare on modern vehicles. My father is a professional mechanic and since the mid/late 80's he can count on one hand I think the number of times the ECU was actually the issue. Lots of people jump to that, replace one and end up wasting money, as is normally the case when people go to part swapping vs full troubleshooting first.
Your static and charge voltages seem fine.
The temp drop to 10V does not seem right, that should not happen, but with a digital meter, possible not so great connections where the leads were connected, etc hard to say that is anything if it never happened again.
A loss of voltage between the alt and battery does not in any way indicate a bad alternator. That is voltage drop in the connections. But, there should not be much of a drop there if the connections are good. As others have stated, make sure ALL power and grounds are good, clean and tight. I would personally start with the grounds.
Your static and charge voltages seem fine.
The temp drop to 10V does not seem right, that should not happen, but with a digital meter, possible not so great connections where the leads were connected, etc hard to say that is anything if it never happened again.
A loss of voltage between the alt and battery does not in any way indicate a bad alternator. That is voltage drop in the connections. But, there should not be much of a drop there if the connections are good. As others have stated, make sure ALL power and grounds are good, clean and tight. I would personally start with the grounds.
09-09-2020, 02:04 PM
#6
09-09-2020, 11:39 PM
#7
This was a pain to get to and I had to take off the valve cover to access it. The connection was a little loose, but not enough for it to start pulling out. I was able to get maybe 1/2 a turn or more with light to moderate pressure. After tightening i applied dielectric grease. Hoping this solves the voltage drop.
Don't forget these cars have Electric load detector what Ecu uses to control charging voltage. https://www.civicforums.com/forums/3...-detector.html
13,8V charging voltage is fine according to S2000 service manual, so alternator is working correctly.
0,2V voltage drop could be bad connection on power wires or ground wires.
13,8V charging voltage is fine according to S2000 service manual, so alternator is working correctly.
0,2V voltage drop could be bad connection on power wires or ground wires.
I think you may be right about the grounds. I noticed obvious corrosion (green stuff) on the ground connected to the driver wheel well. However when i checked the resistance it was less than 0.5 ohms, which i think is ok. I decided to clean it off anyway and applied dielectric grease.
As a reference item, ECU failure is actually pretty rare on modern vehicles. My father is a professional mechanic and since the mid/late 80's he can count on one hand I think the number of times the ECU was actually the issue. Lots of people jump to that, replace one and end up wasting money, as is normally the case when people go to part swapping vs full troubleshooting first.
Your static and charge voltages seem fine.
The temp drop to 10V does not seem right, that should not happen, but with a digital meter, possible not so great connections where the leads were connected, etc hard to say that is anything if it never happened again.
A loss of voltage between the alt and battery does not in any way indicate a bad alternator. That is voltage drop in the connections. But, there should not be much of a drop there if the connections are good. As others have stated, make sure ALL power and grounds are good, clean and tight. I would personally start with the grounds.
Your static and charge voltages seem fine.
The temp drop to 10V does not seem right, that should not happen, but with a digital meter, possible not so great connections where the leads were connected, etc hard to say that is anything if it never happened again.
A loss of voltage between the alt and battery does not in any way indicate a bad alternator. That is voltage drop in the connections. But, there should not be much of a drop there if the connections are good. As others have stated, make sure ALL power and grounds are good, clean and tight. I would personally start with the grounds.
Haven't been able to test yet if the drop to 10V is still happening with the new alternator. However, the drop in voltage is definitely load related. The drop occured when i turned on all the accessories (AC, headlights, etc.), also the loss in EPS usually occurred when i let go of the gas or coming to a stop. Also, in the most recent case when the battery and parking light flashed i was letting go of the gas to make a left turn.
Hoping this is the case. I don't know what else to do if it doesn't work.
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