XAntivenomX

iTrader: (5)

Title pretty much says it all. I get a PO152 intermittently. Most of the time at idle B2S1 is flatlined at about 1060, and the B1S1 will flatline at about 900 or so then weakly oscillate. Sometimes they will flatline at lower voltages. During cruising they will oscillate lost of the time, but sometimes flatline like at idle. But the B2S1 is always about 100mv above B1S1, even when oscillating It's like the graph is shifted upwards 100mv. I have changed out the O2's, and the problem does not follow the sensor. When I unplug the MAF the O2's stay the same, so if it was the MAF, they would change somewhat. I am gonna check out the wiring to the PCM(around the O2's the wires are fine) soon.
Any ideas of what to look for next?

<small>[ February 01, 2003, 09:52 AM: Message edited by: XAntivenomX ]</small>

98TAauto

iTrader: (2)

Ryan, i dont mean to butt into your post but how do you read the MV?? Its probably a stupid question, but I always see posts about .450MV and etc or something like that. It that just what shows up when you log you 02's on atap??

XAntivenomX

iTrader: (5)

Yes, the numbers 890 or 450 whatever is shown is in the units of millivolts(mv).
890mv = .890v

XAntivenomX

iTrader: (5)

ttt, c'mon someone knows about this stuff!

eallanboggs

iTrader: (1)

Are you saying BOTH Bank 1 AND Bank 2 S1s go flatline? You know both O2s don't go bad simultaneously. Especially NOT on an intermittent basis. Now what is in COMMON to both? The wiring harness. The PCM. How does the car perform? Do you have driveability problem? You should if your pre-cat O2s are going flatline. This doesn't sound like it could be caused by another sensor like your MAF. Sure MAF effects the O2s, but it wouldn't make it go flatline. This sounds like a short to ground on your Vcc line. I'd check the wiring harness very carefully. Also check the connector at the PCM. Is it clean and tight? Any chaffing?

XAntivenomX

iTrader: (5)

Thanks for the info, I have been leaning towards a wiring problem. I will post the results after I check stuff out.

And yes, both will flatline, but it is mostly the B2 sensor. I do have driveability problems when the sensors flatline, the car will stumble and not accelerate, then jump forward when the sensors come back to life.

Where is the Vcc line? Is it one of the wires coming out of the PCM?

eallanboggs

iTrader: (1)

All sensor have to have min of 3 wires to work. A HOT wire 12vdc or 5vdc). Ground and a SENSE line. The sense line MONITORS the function of the device (could be VOLTAGE, FREQUENCY, PRESSURE, etc.) If the voltage supply line (Vcc) gets SHORTED to ground this bypasses the LOAD (SENSOR) and should blow a fuse. If the SENSE line shorts to ground it would cause the sensor output to FLATLINE. You have to use a schematic diagram to find the pinouts of the connectors and color codes of the wires that are associated with the sensor you are working on.

XAntivenomX

iTrader: (5)

Any idea what fuse it could blow?
I have the GM service manuals so I will be looking at the pinouts and checking all the wiring.
Thanks for all your help, I figured it was something to do with the wiring, but I am not knowlegeable about these sorts of things, so the explanation helped greatly.

XAntivenomX

iTrader: (5)

Ok, here's an update. I traced the O2 wires yesterday from the O2 back to where it meets the harness on both sides. No burnt wires, nothing out of the ordinary. I looked at the wires coming out of the PCM, took off the PCM connectors, and they were all fine.
I am stumped. Everyone I talk to is stumped. I may be switching PCM's with someone next week to see if that will fix the prob.

JP98SS

I have the same problem. Unless I am on driving around one is peged at 1100mv and the other is right around 350mv. Car stumbles and then takes off. You can feel it loading up.....what was the resolution?

jimmyblue

iTrader: (11)

The oxygen sensor is not like other sensors
that need power. It is given heater power when
needed but this has only indirectly to do with
its output voltage.

It would be good to look at the voltage across
the O2 sensor and see whether this is the same
value as the PCM reports. In systems where the
return for the O2 signal voltage happens to be
the exhaust pipe and engine ground, the PCM's
reading can be offset by ground currents across
the somewhat long and busy path from exhaust
pipe to local chassis ground. Loss of a ground
strap (copper braid from block to fender) can
result in many of the engine-mounted sensors
incurring ground-rise offsets. The sensors
whose return is a separate wire are OK (TPS,
etc.) but anything that presumes the engine
block is 0.0mV from the PCM's reference ground
is subject to this possibility. It wouldn't
hurt to put a DVM from engine block to PCM
chassis and see how much ground discrepancy
there might be.

eallanboggs

iTrader: (1)

That's especially true if you live near a saltwater environment. The resulting rust causes high resistance. People often overlook the importance of a good ground. You are right when you say there could be a difference of potential between the chassis ground and the PCM chassis. They should be bonded securely. This means clean metal surfaces and no rust or corrosion. A good Digital VOM must be used to get an accurate reading. These meters are now available for $29 at Sears.

Steve Burger

iTrader: (33)

Any resolution to this problem. I am having the same issue. I am in the process of tracing wires now.

Team ZR-1

The powertrain control module (PCM) supplies a voltage of approximately 450 mV between the HO2S high and low signal circuits. The heated oxygen sensor varies the voltage from approximately 1,000 mV when the exhaust is rich, to approximately 10 mV when the exhaust is lean.

The PCM monitors and stores the heated oxygen sensor (HO2S) voltage information. The PCM evaluates the HO2S voltage samples in order to determine the amount of time the HO2S voltage was out of range. The PCM compares the stored HO2S voltage samples taken within each sample period, and determines if the majority of the samples are out of the operating range.

The PCM monitors the HO2S voltage for being fixed above a predetermined voltage. If the PCM detects the voltage is above a predetermined voltage, a DTC sets.

The HO2S voltage is more than 775 mV for 165 seconds.

Decel Fuel Cut-off Test
The HO2S voltage is more than 540 mV for 5 seconds.

Action Taken When the DTC Sets
The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.
The control module commands Open Loop.
Conditions for Clearing the MIL/DTC
The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
Clear the MIL and the DTC with a scan tool.
Diagnostic Aids

Important
Before you service the PCM and the throttle actuator control (TAC) module, remove any debris from the module connector surfaces. Inspect the module connector gaskets when you diagnose or replace the modules. Check the gaskets for correct installation. The gaskets prevent contaminate intrusion into the PCM and the TAC modules.
Use the J 35616-A Connector Test Adapter Kit , or use any test that requires probing the PCM or probing a component harness connector. Using this kit prevents damage to the harness and component terminals. Refer to Using Connector Test Adapters in Wiring Systems.

Check the HO2S electrical connections for evidence of water intrusion. Water in the connector causes the B+ supply to the heater to bleed into the signal circuit.
Check the fuel pressure. The system goes rich if the pressure is too high. The PCM compensates for some increase. If the fuel pressure is too high, a DTC may set. Refer to Fuel System Diagnosis .
Check for rich injectors. Perform the Injector Balance Test. Refer to Fuel Injector Balance Test with Tech 2 or Fuel Injector Balance Test with Special Tool .
Check for leaking injectors. Refer to the Fuel System Diagnosis .
Check the evaporative emissions (EVAP) canister purge. Inspect for fuel saturation. If the canister is full of fuel, inspect the canister control and the hoses. Refer to Evaporative Emission (EVAP) Control System Description .
Check the MAF sensor. Disconnect the MAF sensor and see if the rich condition is corrected. If the condition is corrected, inspect for proper installation. If the MAF sensor is correctly installed, replace it. If the MAF sensor is installed backwards, the system goes rich. The plastic portion of the sensor has arrows that indicate the proper air flow direction. The arrows must point toward the engine.
Check the oxygen supply inside the HO2S for proper operation. The HO2S wires provide the supply of oxygen. Inspect the HO2S wires and connections for breaks, or for contamination. Refer to Wiring Repairs in Wiring Systems.
Check for an intermittent condition. Refer to Intermittent Conditions .
Test Description
The numbers below refer to the step numbers on the diagnostic table.

If the voltage is fixed above the specified value, the condition is present.

Using the Freeze Frame/Failure Records data may help to locate an intermittent condition. If you cannot duplicate the DTC, the information included in the Freeze Frame and/or Failure Records data can help to determine how many miles have occurred since the DTC set. The Fail Counter and Pass Counter can also help to determine how many ignition cycles that the diagnostic reported a pass and/or a fail. Operate the vehicle within the same Freeze Frame conditions that the PCM recorded:

The RPM
The vehicle load
The vehicle speed
The temperature This procedure isolates when the DTC failed.
If the voltage remains high, the signal circuit is shorted to voltage.

Step
Action
Value(s)
Yes
No

Schematic Reference: Engine Controls Schematics

1
Did you perform the Diagnostic System Check-Engine Controls?
--
Go to Step 2
Go to Diagnostic System Check - Engine Controls

2
Start and run the engine until normal operating temperature is reached.
With a scan tool, observe the HO2S voltage for the sensor that applies to this DTC.
Is the HO2S voltage more than the specified value?
775 mV
Go to Step 4
Go to Step 3

3
Observe the Freeze Frame/Failure Records data for this DTC.
Turn OFF the ignition for 30 seconds.
Start the engine.
Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text or as close to the Freeze Frame/Failure Records data that you observed.
Does the DTC fail this ignition?
--
Go to Step 4
Go to Diagnostic Aids

4
Turn OFF the ignition.
Disconnect the HO2S connector for the sensor that applies to this DTC.
Jumper the HO2S low signal circuit terminal on the engine harness side to a known good ground.
Turn ON the ignition, with the engine OFF.
Observe the HO2S voltage with a scan tool.
Is the HO2S voltage within the specified range?
350-550 mV
Go to Step 5
Go to Step 6

5
The HO2S may be detecting a rich exhaust condition or may be contaminated. Check for the following conditions:
Water intrusion into the HO2S connector
Silicone contamination of the HO2S
Engine oil contaminated by fuel
Incorrect fuel pressure
Rich fuel injectors
Inaccurate MAF sensor
EVAP canister purge condition
Repair any of the above or similar engine conditions as necessary.
Did you find and correct the condition?
--
Go to Step 11
Go to Step 7

6

Important
The sensor may be damaged if the circuit is shorted to a voltage source.


Turn OFF the ignition.
Disconnect the PCM connector that contains the HO2S high signal circuit. Refer to Powertrain Control Module (PCM) Replacement .
Turn ON the ignition with the engine OFF.
Test the HO2S high signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
--
Go to Step 11
Go to Step 8

7
Inspect for poor connections at the harness connector of the HO2S. Refer to Testing for Intermittent and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?
--
Go to Step 11
Go to Step 9

8
Inspect for poor connections at the harness connector of the PCM. Refer to Testing for Intermittent and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?
--
Go to Step 11
Go to Step 10

9
Replace the affected HO2S. Refer to Heated Oxygen Sensor (HO2S) Replacement Bank 1 Sensor 1 or refer to Heated Oxygen Sensor (HO2S) Replacement Bank 2 Sensor 1 .

Did you complete the replacement?
--
Go to Step 11
--

10
Replace the PCM. Refer to Powertrain Control Module (PCM) Replacement .

Did you complete the replacement?
--
Go to Step 11
--

11
Clear the DTCs with a scan tool.
Turn OFF the ignition for 30 seconds.
Start the engine.
Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.
Does the DTC run and pass?
--
Go to Step 12
Go to Step 2

12
With a scan tool, observe the stored information, Capture Info.

Does the scan tool display any DTCs that you have not diagnosed?
--
Go to Diagnostic Trouble Code (DTC) List
System OK