Sporadic O2 Code with load only in S4
11-22-13, 03:54 PM
#1
Living Large & Loving It
Thread Starter
Join Date: Jul 2011
Location: Land of 10,000 Lakes
Posts: 25
Likes: 0
Received 0 Likes
on
0 Posts
Sporadic O2 Code with load only in S4
I've had the CEL lights installed in the cab of my unmodified S4 NA Sport for a decade and have never seen anything beyond the 3 light initiations. Now I am getting a "5" (2 second on, 2 second off) for an O2 sensor but it only appears randomly. I have seen it light once and stop, more than 30 times and stop and everything in between. Sometimes it is off for a couple of minutes while driving and it never starts at idle.
I did the easy stuff. Replaced the rather new Bosch O2 sensor with an OE NTK sensor with no change in behavior. I checked the voltage at the CPU on the sensor and recorded the usual values that I still don't understand (about .7 vdc at idle and going negative -.1 at about 2K RPM). In 15 minutes of idling while checking voltages the CEL never lit. As soon as I drive down the street I get the "5" but the voltage on the O2 is still registering at -.1. Of course the voltages are changing constantly as RPM's change, so I'm simplifying the observed values.
I have a general understanding about the closed loop system that kicks in somewhere around 1500 RPM's but I am at a loss to explain this code. Does the closed loop system initiate when revving at a standstill and is this code related? I know I'm being a perfectionist once again as this great car seems to still run perfectly. Any good ideas would certainly be welcome.
I did the easy stuff. Replaced the rather new Bosch O2 sensor with an OE NTK sensor with no change in behavior. I checked the voltage at the CPU on the sensor and recorded the usual values that I still don't understand (about .7 vdc at idle and going negative -.1 at about 2K RPM). In 15 minutes of idling while checking voltages the CEL never lit. As soon as I drive down the street I get the "5" but the voltage on the O2 is still registering at -.1. Of course the voltages are changing constantly as RPM's change, so I'm simplifying the observed values.
I have a general understanding about the closed loop system that kicks in somewhere around 1500 RPM's but I am at a loss to explain this code. Does the closed loop system initiate when revving at a standstill and is this code related? I know I'm being a perfectionist once again as this great car seems to still run perfectly. Any good ideas would certainly be welcome.
11-22-13, 08:24 PM
#2
Living Large & Loving It
Thread Starter
Join Date: Jul 2011
Location: Land of 10,000 Lakes
Posts: 25
Likes: 0
Received 0 Likes
on
0 Posts
Afterthoughts:
I disconnected the O2 sensor and the result was as you would expect. A constant "5", so I'm guessing the wire is good on that sensor.
There is an excellent CALPATRIOT description of testing the open/closed loop mode, but since I don't have any performance issues I'm not expecting a problem. Still, I'll try it when it warms up a little in this state.
https://www.rx7club.com/2nd-generati...ast-2k-856697/
I disconnected the O2 sensor and the result was as you would expect. A constant "5", so I'm guessing the wire is good on that sensor.
There is an excellent CALPATRIOT description of testing the open/closed loop mode, but since I don't have any performance issues I'm not expecting a problem. Still, I'll try it when it warms up a little in this state.
https://www.rx7club.com/2nd-generati...ast-2k-856697/
11-30-13, 07:52 PM
#3
Living Large & Loving It
Thread Starter
Join Date: Jul 2011
Location: Land of 10,000 Lakes
Posts: 25
Likes: 0
Received 0 Likes
on
0 Posts
Thanks to the 72 of you that have read about this issue, but I guess I stumped you too. I learned some more, but it's not solved yet.
I plugged-in a open/closed loop test lamp so that I could monitor while driving with a warm engine.
Accelerating = On (good)
Decelerating = Off (good)
Cruising at speed = Off (not good)
Idling = Off (not sure, but CALPATRIOT's was On)
In the last 70 miles I only saw the lamp briefly blink like it should one time and it was at idle.... not good.
I tried reseating the connectors into the CPU and we'll see if that does anything, but confidence is low on that one. I can't believe it's an oxygen sensor wire since I'm getting voltages, albeit odd ones, when I pin the back of the plug at the CPU. I'll keep trying things when I get another warm day.
I plugged-in a open/closed loop test lamp so that I could monitor while driving with a warm engine.
Accelerating = On (good)
Decelerating = Off (good)
Cruising at speed = Off (not good)
Idling = Off (not sure, but CALPATRIOT's was On)
In the last 70 miles I only saw the lamp briefly blink like it should one time and it was at idle.... not good.
I tried reseating the connectors into the CPU and we'll see if that does anything, but confidence is low on that one. I can't believe it's an oxygen sensor wire since I'm getting voltages, albeit odd ones, when I pin the back of the plug at the CPU. I'll keep trying things when I get another warm day.
12-02-13, 04:43 PM
#5
Living Large & Loving It
Thread Starter
Join Date: Jul 2011
Location: Land of 10,000 Lakes
Posts: 25
Likes: 0
Received 0 Likes
on
0 Posts
Satch, you've helped me before. Thanks again.
I was about to ask what are all the things that must be in place to initiate closed loop and there's my answer. I had just tested a new wire on the O2 sensor and, not surprisingly, it made no difference. I had already jumpered the clutch switch weeks ago, but now I've got several new items to verify.
I was about to ask what are all the things that must be in place to initiate closed loop and there's my answer. I had just tested a new wire on the O2 sensor and, not surprisingly, it made no difference. I had already jumpered the clutch switch weeks ago, but now I've got several new items to verify.
12-03-13, 02:22 PM
#6
Living Large & Loving It
Thread Starter
Join Date: Jul 2011
Location: Land of 10,000 Lakes
Posts: 25
Likes: 0
Received 0 Likes
on
0 Posts
Problem solved after learning that both the clutch and neutral switches are also involved in closed loop mode. It turns out I shot myself in the tit on this one. I had been working on a rare but re-occurring "sticky starter issue" and I jumpered the clutch switch as suggested below just to eliminate the possibility. The link is included in the '86 to '92 section, so maybe the conversation relates to a later model than my S4. At any rate, jumpering the clutch switch does not produce the desired effect in an '86.
https://www.rx7club.com/2nd-generati...-896013/page7/
Once I referred to my well-worn actual '87 FSM for my '86 vehicle that I own from the days before there was an Internet, it explains that continuity in the clutch switch occurs when the clutch is depressed (i.e. neutral). So, my ECU saw the car in neutral all the time because of the jumper. I plugged the switch back in and the O2 sensor code is gone and closed loop runs as it should.
I know, I know, spare me the wisecracks. At least I'm bold enough to admit my amateurish mistake. And in my own defense, the car isn't driven a lot so I missed the connection. Happy smog-free cruising.
https://www.rx7club.com/2nd-generati...-896013/page7/
Once I referred to my well-worn actual '87 FSM for my '86 vehicle that I own from the days before there was an Internet, it explains that continuity in the clutch switch occurs when the clutch is depressed (i.e. neutral). So, my ECU saw the car in neutral all the time because of the jumper. I plugged the switch back in and the O2 sensor code is gone and closed loop runs as it should.
I know, I know, spare me the wisecracks. At least I'm bold enough to admit my amateurish mistake. And in my own defense, the car isn't driven a lot so I missed the connection. Happy smog-free cruising.
Thread
Thread Starter
Forum
Replies
Last Post
Linda_Lovelace
General Rotary Tech Support
0
09-18-15 10:04 PM