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P0136 code
Topic Started: Jun 6 2010, 01:17 AM (3,018 Views)
Bill CNC
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Hi Guy's

I was coming home from the pet store today and my engine light popped on. While driving, (probably not a safe thing to do) I used my newly installed ScanGauge to read the code, ... P0136.

I looked at the sticky here Check Engine Light Codes and it says, "P0136 - HO2S 2 Circuit Malfunction".

Rear O2 ????
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Bill CNC
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I cleared the code and drove for about 20 miles with more than half of the drive, ... above 55MPH. I was unable to trigger the engine light again.

Any clues?
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Woodie
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PCM doesn't like the voltages it sees from O2 sensor #2. Could be a bad ground or poor electrical connection, could also be an exhaust leak or water intrusion. Might take quite a while for conditions to be just right to run the test again: Engine speed over 1,500, Vehicle speed between 20 and 50,Coolant temp over 176°, Intake air temp 14° to 158°, Barometric pressure above 75 kPa, fuel tank over 25%, engine running in closed loop mode. If all these criteria are met, and it sees less than 600mv for at least 8 minutes, that's the error. Or if it sees more than 300mv during fuel shutoff mode.

Set your ScanGauge to read O2 #2 voltage and go for a drive. It should read 1.25 V while cold. Once it warms up it should fluctuate from 100 to 900 mV.
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Bill CNC
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Woodie
Jun 6 2010, 06:40 AM
Set your ScanGauge to read O2 #2 voltage and go for a drive. It should read 1.25 V while cold. Once it warms up it should fluctuate from 100 to 900 mV.
Woodie,

Thanks for the response. I am still new to the ScanGauge, and I'm not sure I can read the o2 sensors, or how to get it if it can read it. I haven't found an o2 gauge.

Do you know how?
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mwebb
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FOG

the scangauge 2 is a generic ODB2 scan tool
there should be a list of PIDs parameter I D s that are available for viewing , scroll through the
live data
PIDs
or choice C something similar

list to find

Rear 02 sensor voltage or something that is very similar
and
Rear 02 sensor heater condition / state

the rear 02 sensor heater does Not switch on until about 50mph , after it has switched on it stays on until the engine cools off , as long as the key is in the "on " position
if you turn the key to off then back to on , the rear 02 heater will be enabled .
after the engine cools off , you will need to drive faster than 50 mph to enable the rear 02 sensor heater .
the rear 02 sensor does not function if the heater is disabled , voltage will be high .

like this
Posted Image

if you never exceed 50 mph the rear 02 sensor heater never switches to on
and
the rear 02 sensor never begins to function
so then
the system can not test it and fail it and code for the failure .
the CEL (check money) light , never comes back on.

if
the rear 02 sensor is connected and not installed in the exhaust but instead left in the little pocket by the upper RF strut bearing
then
the CEL (check money) light , never comes back on. and the CAT monitor will still run and pass ?
this is a conflict and should be false , yet it is true .

assuming the rear 02 sensor is functioning as designed
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mwebb
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FOG

the moral of this story is

never go to the pet store .
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Spock
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Live Long and Prosper.

MWebb,

A little off topic, but is seems like you are the guy to ask. Do you believe that O2 sensors can become 'lazy' before they fail altogether? Also, would a symptom of this be poor fuel economy? I don't have an oscilloscope in my garage, so please dumb it down a little for me :drool

Rob
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mwebb
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FOG

MetroRob
Jun 6 2010, 08:57 PM
MWebb,

A little off topic, but is seems like you are the guy to ask. Do you believe that O2 sensors can become 'lazy' before they fail altogether? Also, would a symptom of this be poor fuel economy? I don't have an oscilloscope in my garage, so please dumb it down a little for me :drool

Rob
yes .
maybe FE would suffer . depends .

if the failing 02 sensor was biased OR took too long to switch one way while it switched normally the other way
yes .

the 02 sensor must switch from 150 to 850 mv at 2k rpm hot
the 02 sensor must switch from 850 to 150mv at 2k rpm hot
average 450mv with equal time above and below 450mv
in the pattern of a sine wave.

if you do not have a scope
on OBD2 some systems will test the 02 sensor (s) and display the results in either Mode 5 or Mode 6 test results .
results that are farthest from the test limits are better
see "GM MODE 6" to read more .

you need a scope

you can use a better DVOM on MIN MAX , average should be 450mv and min about 100mv and max about 900mv
but
that will not be accurate ,
you need a scope
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Woodie
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My O2 sensor heaters both switch on the instant the car is started. They might switch off later, I don't know. The entire point of the heater is to get the sensors up and running so the car could get into closed loop as fast as possible.
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mwebb
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FOG

Woodie
Jun 7 2010, 04:49 AM
My O2 sensor heaters both switch on the instant the car is started. They might switch off later, I don't know. The entire point of the heater is to get the sensors up and running so the car could get into closed loop as fast as possible.
Mr ECM does not need any input from the rear 02 sensor to go to closed loop
UNLESS the system trims on the rear 02 sensor as well

the earlier G10s and G13s do not

all the metros and swifts i have worked on do not have an active PID for

Rear 02 sensor fuel trim

but
i have not worked on a 1998 G13 like Woodie's

for future refrence
it would be great to know IF there is a valid PID for rear 02 sensor trim on Woodie's car
if there is the value should be about the same as LTFT
or
Front 02 sensor fuel trim
and may change slightly as the load on the engine changes
if the PID is valid the value will only be zero right after clearing DTCs or possibly on start up
when the system is HOT and driving
the value should Never be zero when the system is in closed loop

if the value is 100% the PID is not valid
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Woodie
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What's PID?

One of the tests for O2 heater failure is to unplug the sensor, turn on the key and measure the voltage being sent to the heater. No mention of warming the car up.
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mwebb
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FOG

Woodie
Jun 8 2010, 05:32 AM
What's PID?

One of the tests for O2 heater failure is to unplug the sensor, turn on the key and measure the voltage being sent to the heater. No mention of warming the car up.
PID = Parameter ID
each line of scan data has a "name / Label" that is a PID

best not to test the 02 sensor heater when the sensor is disconnected
if there is a voltage drop on either circuit the open circuit results will be UN valid .

best to use T pins on the two white wires -
on the connectors without piercing the wire without disconnecting the connector

white wires are heater either could be any polarity but they must be opposite polarity to the other white wire
, black is signal , gray is 02 sensor ground
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Woodie
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That was straight from the FSM. Next test is to use an ohmmeter to check the heater itself.
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