O2 sensor heater reads 7.5 volts / emission failed

[Andrew99]

Hello:

So my car (cal spec) fails emissions. Elanscan shows the O2 sensor a steady 2 volts.
I put in a new sensor and it looks the same. I do a "torch /Ohm meter"test on the
two sensors and the new sensor reads good and the old sensor reads about 80%.
I drove the car around a bit with Elanscan running and and the O2 starts working
normal after about 10 minutes of driving. This lead me to the O2 sensors heater circuit.
One of the wires has a good ground and the other a constant 7.5 volts DC. Documentation
from WikiLEC says it should be 12 volts.

Question is the 02 sensor heater voltage controled by the ECM? Could another sensor
malfunction be causing the ECM to lower the O2 sensor voltage?

thx,
Andrew

[GeoffSmith]

Andrew, I've put some more information in the Wiki about the wiring and a circuit diagram. If your charge light is on then the heater is not driven at 12 V - if you increase the revs so the light goes out, you should get 12V.

[Andrew99]

new o2 2013 part1.zip

I tried to find the charge light circuit but was unable.
The Isuzu O2 sensor is controlled by the ECM as shown below:
I'm thinking that the Californian M100 might be the same.


P0030 ISUZU Description
Oxygen Sensors (O2S) or Heated Oxygen Sensors (HO2S) need to reach a minimum operating temperature of 750 degrees F to produce an accurate voltage signal. The faster the heated oxygen sensor reaches that temperature the faster the sensor will start sending an accurate signal to the Engine Control Module (ECM).
In order to achieve the require temperature, a heater element is included inside the heated oxygen sensor. The ECM controls the heated oxygen sensor heater element based on signals from the engine coolant temperature and engine load. The ECM controls the heater element circuit by allowing current flow to ground.
The ECM monitors the voltage signal received through the heater element circuit and determines the state of the circuit by comparing the voltage detected with the factory specifications.

If so "the ECM heater voltage" should be in the Elanscan but I can not find it.

Maybe someone could find another problem in my attached scan that is causing my high emissions.
Even at 7.5 volts the O2 sensor does seems to work once at full temp. And my Temp gauge was a bit
over have way up during the emissions test.

thx,

Andrew

[GeoffSmith]

This figure in the Wiki is from the EMJ4 "Electronic MPFI (Closed Loop) Elan Turbo with Catalyst" and no Elan variants are configured like the Isuzu.

Anyway, your sensor is heating up in ~100s which is fine but when you're idling (between 300s and 550s) the low output is drifting up from 0V resulting in the engine reverting to open loop - see the Closed Loop Flag #42 bit 0. I suspect that the heater is not working properly when idling which is why you fail the emissions test. When the engine is under load, the exhaust gases are hot enough to keep the sensor working and it runs closed loop. Can you hook up a meter across the heater to confirm the voltage?

[Brit-Car-Nut]

Andrew: Have you verified that the fuel pressure is correct and the injectors are outputting a proper spray? My car developed a rich state and I ended up replacing the fuel pump, pressure regulator and sending the injectors out to be tested and cleaned. It is running well now although I don't need to be somg tested in NC.

The pre-OBD1 injection doesn't keep track of many of the issues the later OBD2 systems do and your car might be running rich, then lean when overcorrected by the ECM and then rich again. Since the ECM varries the ground signal to the HO2S based on wht it is "reading", it might be other things "confusing" the ECM to keep the HO2S running cooler. Anything like a CTS running off spec to excessive fuel pressure could compound the ECM's confusion.

[GeoffSmith]

The heater is not controlled by the ECU:

[Simon_P]

Geoff,

Your earlier post has got me looking at my elanscan results.

Please could you confirm if Flag 42 = off is closed or open loop?

[GeoffSmith]

Flag42-bit0 high means it is closed loop. If you look at when the engine comes on boost, this flag always drops out as the ecu goes open loop.

[Andrew99]

I compared my scan to a posted known good scans from here.
They all seem to (once at temp) fluctuate from open to closed
loop at idle.

I'm thinking I could test wire 12 volts straight from the battery and
see if the scan if different.

Thanks again for all the help

Andrew

[Simon_P]

Thanks Geoff!

I have a scan of a start from cold until the fans come on.

Flag 42 is always 0. Hence my question - something isn't right!
It does go to 1 with the Turbo as described.

[Andrew99]

update:

Ran a wire from the battery to the O2 sensor heater. Elanscan shows the Sensor start to swing from 0 to 4 volts
sooner than before, but does not go Closed Loop at idle (5 minutes). With an Ohm meter on the heater it still reads 7.5 volt
with out the wire from battery. Driving around the ohm meter it starts to read up to 9.7 volts after about
5 minutes (goes Closed Loop) then back to 7.5 at idle. Comparing Flag 42 with the other lines in the scan the EGR valve
moves one to one with the Closed Loop bit as does some unlabeled flags. I can not see the sensor or combination of sensors
that triggers the system to go Closed Loop.

Thx for reading,

Andrew

[GeoffSmith]

Check the heater earth. Sound like it isn't at 0V if you're measuring less than 12V across it with a solid 12V connection.

[Andrew99]

It reads a solid 12volt with the wire from the battery. I just didn't drive it around that way.

[Simon_P]

I compared my scan to a posted known good scans from here.
They all seem to (once at temp) fluctuate from open to closed
loop at idle.

Can you point me to the known good scans please.

[Andrew99]

After finding the source of the scan I was using for comparison, seems his car was also having O2 sensor problems:
I emailed the poster of this scan to see if he has an "after fix" one.

viewtopic.php?f=34&t=19915

This is the only scan that I've found that has a Flag 42 reading.

If someone has one, Please post it.

[GeoffSmith]

A good O2 trace, shame about the stuck thermostat!

Geoff 2011 04 16 Stuck thermostat Part 2.zip

[Andrew99]

Geoff your trace also looks like it goes open loop at idle (the last 50 sec).

[tomatcbl]

Geoff your trace also looks like it goes open loop at idle (the last 50 sec).

I posted the elanscan that Andrew referred to. I could never find any electrical solution to the open/closed issue. Most recent fail was in Feb 2013. The next day, I had an injector failure - a previous owner of my car had used oversized injectors (375 cc) and when one of them fouled, I took the opportunity to replace the injectors with standard size ones (RC Engineering 320 cc). When I took it back, the car passed. I have not hooked it up to Elanscan since, but will do so this weekend and post what I have now.

[Andrew99]

Heater voltage problem is solved!

Voltage is now 12.2 volts with the key on and 13.5 when running.
Though the Closed loop scans look the same. Car goes Open loop at idle.

The O2 heater voltage comes from the brown yellow stripe wire on the alternator
the alternator read 13 volts at the gauge and would charge the battery but the
brown/yellow was 7.5 volts. Original alternator must have had some internal
regulator problem...

I had read some reports that Isuzu alternators were bigger than the Lotus ones
and would not fit. I bought a 91 impulse RS alternator from Autozone. They
had it in stock at my local store. Looking at them side by side they seemed
the same size though I did not measure them. Putting it in was no easy task.
I took off the engine mount and jacked the engine around a bit to get it in.
but the hard part is getting the cables reconnected! I'd say a timing belt is
an easier job than an alternator on a M100.

I'm looking forward to seeing if Tom's scan shows that his car goes Open Loop
at idle after he passed his emissions test.

Andrew

[HJ2]

I had read some reports that Isuzu alternators were bigger than the Lotus ones
and would not fit. I bought a 91 impulse RS alternator from Autozone. They
had it in stock at my local store. Looking at them side by side they seemed
the same size though I did not measure them. Putting it in was no easy task.
I took off the engine mount and jacked the engine around a bit to get it in.
but the hard part is getting the cables reconnected! I'd say a timing belt is
an easier job than an alternator on a M100.

When you have the OEM alternator this is not entirely (but almost!) true
The Isuzu one is only 6 mm bigger and won't get past the suspension parts (unless one does what you did )

The OEM goes back with a little encouraging, but without the need to remove the engine support


Good that you solved the voltage problem!
Regulator packs tend to go a little early due to the hot & tight space where the alternator sits.