I'm trying to solve a problem for someone, and it'* being turned into a million dollar workup by other forces. It'* a '97 L67 and he'* getting nothing from boost.

50% TPS
MAP is reading @100 kpa (30 inHG) (This is the same as my My '98 L67 gets)

100% TPS
MAP reading @ 112 kPa

(Both of the above show MAF intake which indicate normal operation.)

BOTH of his O2 sensors are reading .96, with virtually no toggle to Lean which is usually near .1.

His Fuel Trims are (somehow) well within +/-6.

The ignition advance is going to -20*.

This all started after he stored it for 6 months, in a barn.
He'* just had the DP and cat replaced. Thinking of a back pressure problem
He has a ZZP 1.0 PCM.

During problem solving he got a P0141 O2 Sensor Heater Circuit Malfunction (Sensor 2), which means his S2 O2 sensor heating unit is not heating enough or is taking too long to heat up. From reading the FSM, I think it'* saying that the S1 O2 sensor to PCM operation will not activate if there is an S2 O2 sensor failure. In other words, he might not go Closed Loop. I'm not sure of that.

It'* making me crazy because his scantool can't give him things like an EGR reading or whether the Loop is Closed or not. Or Opens at WOT.

My first reaction was to tell him to get the O2'* replaced just on general principles. So we know what we are working with, and they are probably worthless anyway. That got voted down by other problem solvers. Ok, then my next best guess is that the */C Boost Control Actuator is not cutting in the */C. (I'm trying to get him to test that, now.)

Here'* my other issue, the PCM should be throwing a (some) DTC over the low voltage from the MAP at WOT.. and should be equally angry about the barely moving .9+ S1 O2 sensor reading.

I hope that is enough info for some detective work. It'* kinda past my area of confidence as it'* getting into where you high performance guys spend your time, even though it'* a problem issue and not a performance enhancement/tuning.

Any thoughts would be a big help. Thanks.

edit: Sorry, I proofed the original post, But still got the O2 sensor DTC wrong, now it is correct.

Here is some diagnostic for a boost control check. I could not find a diagnostic for p1440 or anything concerning ho2s.
Hope this will get you somwhere. I am not sure how readable this will be haven't figured out the best way to get these pages copied yet. Just remember goto for yes is always first.


Document ID# 47530
1997 Pontiac Bonneville


--------------------------------------------------------------------------------

Boost Control System Check




(1) By-Pass Valve Actuator
(2) Boost Signal
(3) Boost Control Solenoid
(4) Boost Source
(5) Supercharger
(6) Intake Plenum
(7) By-Pass Valve
( Throttle
(9) Air Cleaner
(10) MAF Sensor
(11) Inlet Vacuum Signal

Circuit Description
Under most conditions, the PCM commands the boost control solenoid to operate at a 100 percent duty cycle (ON) to allow full boost pressure upon demand. However, if reverse gear is selected or the PCM detects rapid deceleration or engine load is extremely high, reduced boost pressure is desired. Under these conditions, the PCM commands the boost control solenoid to operate at a 0 percent duty cycle (OFF), which opens the bypass valve. With the Bypass valve open, boost pressure is reduced by recirculating intake air back through the supercharger inlet.

Boost Control System Hose Routing




(1) Vacuum Signal to Bypass Valve Actuator
(2) Boost Signal to Fuel Pressure Regulator
(3) Bypass Valve Actuator
(4) Boost Signal to Bypass Valve Actuator
(5) Boost Control Solenoid
(6) Boost Source to Boost Control Solenoid

Diagnostic Aids
If the Boost Control System Check has been performed and no electrical or vacuum related fault is noted, check for the following conditions:

Misadjusted or sticking Bypass Valve Actuator. Refer to Bypass Valve Actuator
Binding Bypass Valve or Bypass Valve linkage. Refer to Supercharger section 6G.
An intermittent may be caused by a poor connection, rubbed through wire insulation, or a wire broken inside the insulation. Check for the following conditions:

Poor Connection or Damaged Harness - Inspect PCM harness connector for backed out terminals, improper mating, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.
Intermittent Test - Disconnect PCM and install a DVM to monitor voltage between the Boost Control Solenoid control circuit at the PCM connector and ground. With the key ON, observe voltage while manipulating related connectors and wiring harness. If the failure is induced, the voltage display will change. This may indicate the location of the fault
Test Description
Number(*) below refer to the step number(*) on the Diagnostic Table.

Verifies ignition feed to the boost control solenoid.

The boost control solenoid should be commanded OFF (0% duty cycle) with the ignition ON, engine not running. If the system is functioning properly, the test light should be OFF.

Ensures that the PCM can control the ODM output for the Boost Control Solenoid and the Boost Control Solenoid control circuit is not open.

Checks for a malfunctioning Boost Control Solenoid (sticking open or leaking).

This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed.

Boost Control System Functional Check (VIN 1 Only) Step
Action
Value(*)
Yes
No

1
Was the On-Board Diagnostic (OBD) System Check performed?
--
Go to Step 2
Go to the Powertrain On Board Diagnostic (OBD) System Check

2
Disconnect the Boost Control Solenoid electrical connector.
Turn ON the ignition switch.
Install a test light between the ignition feed circuit at the Boost Control Solenoid harness connector and engine ground.
Is the test light ON?
--
Go to Step 3
Go to Step 11

3
Connect the test light between the Boost Control Solenoid harness connector terminals.

Is the test light ON?
--
Go to Step 14
Go to Step 4

4
Select Boost Control Solenoid output control with scan tool.
Observe the test light while turning the Boost Control Solenoid output ON with the scan tool.
Is the test light ON when the Boost Control Solenoid output is commanded ON?
--
Go to Step 5
Go to Step 16

5
Reconnect the Boost Control Solenoid electrical connector.
Disconnect the boost signal hose between the Boost Control Solenoid and the Bypass Valve Actuator. Refer to Boost Control System Hose Routing .
Connect a vacuum gauge to read the boost signal from the Boost Control Solenoid.
Start the engine and idle in Park.
Observe the vacuum gauge reading.
Does the vacuum gauge indicate near the specified value?
0 in. Hg
Go to Step 6
Go to Step 17

6
Turn the Boost Control Solenoid OFF with the scan tool.
Observe the vacuum gauge.
Does the vacuum gauge indicate greater than the specified value with the Boost Control Solenoid turned OFF?
15 in. Hg
Go to Step 7
Go to Step 10

7
Check for a restriction in the boost signal hose between the Boost Control Solenoid and the Bypass Valve Actuator. Refer to Boost Control System Hose Routing .
If a problem is found, repair as necessary.
Was a problem found?
--
Go to Step 21
Go to Step 8

8
Reconnect the boost signal hose between the Boost Control Solenoid and the Bypass Valve Actuator.
Connect the vacuum gauge to read the inlet vacuum signal to the Bypass Valve Actuator. Refer to Boost Control System Hose Routing .
Start the engine and idle in Park.
Observe the vacuum gauge reading.
Does the vacuum gauge indicate greater than the specified value?
15 in. Hg
Refer to Diagnostic Aids
Go to Step 9

9
Repair the restriction in the inlet vacuum signal hose to the Bypass Valve Actuator or blocked inlet vacuum source. Refer to Boost Control System Hose Routing .

Is action complete?
--
Go to Step 21
--

10
Check for a restriction in the boost source hose to the Boost Control Solenoid. Refer to Boost Control System Hose Routing .
If a problem is found, repair as necessary.
Was a problem found?
--
Go to Step 21
Go to Step 18

11
Check the fuse for the Boost Control Solenoid ignition feed circuit.

Is the fuse blown?
--
Go to Step 12
Go to Step 13

12
Locate and repair short to ground in the ignition feed circuit. Refer to Repair Procedures in Electrical Diagnosis.

Is action complete?
--
Go to Step 21
--

13
Locate and repair open in the ignition feed circuit to the Boost Control Solenoid. Refer to Repair Procedures in Electrical Diagnosis.

Is action complete?
--
Go to Step 21
--

14
Turn OFF the ignition switch.
Disconnect the PCM.
Turn ON the ignition switch.
Observe the test light connected between the Boost Control Solenoid harness connector terminals..
Is the test light ON?
--
Go to Step 15
Go to Step 20

15
Locate and repair short to ground in the Boost Control Solenoid control circuit. Refer to Repair Procedures in Electrical Diagnosis.

Is action complete?
--
Go to Step 21
--

16
Turn OFF the ignition switch.
Disconnect the PCM.
Turn ON the ignition switch.
Check the Boost Control Solenoid control circuit for an open or a short to voltage.
If a problem is found, repair as necessary. Refer to Repair Procedures in Electrical Diagnosis.
Was a problem found?
--
Go to Step 21
Go to Step 19

17
Check for poor terminal connections at the Boost Control Solenoid.
If a problem is found, repair as necessary. Refer to Repair Procedures in Electrical Diagnosis.
Was a problem found?
--
Go to Step 21
Go to Step 18

18
Replace the Boost Control Solenoid. Refer to Boost Control Solenoid .

Is action complete?
--
Go to Step 21
--

19
Check the Boost Control Solenoid control circuit for a poor terminal connection at the PCM.
If a problem is found, repair as necessary. Refer to Repair Procedures in Electrical Diagnosis.
Was a problem found?
--
Go to Step 21
Go to Step 20

20
Replace the PCM.


Important
Replacement PCM must be programmed. Refer to PCM Replacement/Programming .


Is action complete?
--
Go to Step 21
--

21
Disconnect the inlet vacuum signal line from the bypass valve actuator. Refer to Boost Control System Hose Routing .
Engine idling.
Select output tests, Boost Sol. on the scan tool.
Observe MAP reading on the scan tool while cycling the boost solenoid ON and OFF.
Does the MAP value decrease while the boost sol. is commanded ON and increase while the boost sol. is commanded OFF?
--
Go to Step 22
Go to Step 2

22
Reconnect the inlet vacuum signal line to the bypass valve actuator. Refer to Boost Control System Hose Routing .

Is action complete?
--
System OK
--

I think I may have found something that might help with your ho2s.
Let me know if this helps.

Document ID# 46883
1997 Pontiac Bonneville


--------------------------------------------------------------------------------

DTC P0140 HO2S Circuit Insufficient Activity Sensor 2




Circuit Description
The powertrain control module (PCM) supplies a bias voltage of about 450 mV between the HO2S high and low signal circuits. When measured with a 10 megohm digital voltmeter, this may display as low as 320 mV. The oxygen sensor varies the voltage within a range of about 1000 mV when the exhaust is rich, down through about 10 mV when exhaust is lean. The PCM constantly monitors the HO2S signal during closed loop operation and compensates for a rich or lean condition by decreasing or increasing injector pulse width as necessary. If the HO2S 2 voltage remains at or near the 450 mV bias for an extended period of time, DTC P0140 will be set, indicating an open sensor signal or sensor low circuit.

Conditions for Setting the DTC
No EGR, Transaxle, TP sensor, EVAP system, misfire, IAT sensor, MAP sensor, fuel trim, fuel injector circuit, ECT sensor, or MAF sensor DTC(*) present.
Engine run time greater than 200 seconds.
HO2S 1 signal voltage remains between 425 mV and 474 mV for longer than 100 seconds.
Action Taken When the DTC Sets
The PCM will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed.
The PCM will store conditions which were present when the DTC set as Freeze Frame and Failure Records data.
Conditions for Clearing the MIL/DTC
The PCM will turn OFF the MIL during the third consecutive trip in which the diagnostic has been run and passed.
The History DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
The DTC can be cleared by using the scan tool.
Diagnostic Aids
Check for the following conditions:

Corroded exhaust flange attaching hardware. Using a digital multimeter, ensure that continuity exists between the engine block and the heated oxygen sensor shell. If resistance is excessively high (over 500 ohms), replace corroded exhaust flange attaching hardware as necessary. Refer to Front Pipe Replacement in Engine Exhaust.
Poor connection or damaged harness. Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness.
Malfunctioning HO2S heater or heater circuit. With the ignition ON, engine not running the HO2S voltage displayed on a scan tool should drop to less than 250 mV or rise to above 600 mV within 2 minutes. If not, disconnect the HO2S and connect a test light between the HO2S ignition feed and heater ground circuits. If the test light does not light, repair the open ignition feed or sensor ground circuit as necessary. If the test light lights and the HO2S signal and low circuits are OK, replace the affected HO2S.
Intermittent test. With the ignition ON, monitor the HO2S signal voltage while moving the wiring harness and related connectors. If the malfunction is induced, the HO2S signal voltage will change. This may help isolate the location of the malfunction.
Test Description
Number(*) below refer to the step number(*) on the Diagnostic Table:

If the DTC P0140 test passes while the Fail Records conditions are being duplicated, an intermittent condition is indicated.

Reviewing the Fail Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.

This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed.

DTC P0140 - HO2S Circuit Insufficient Activity Sensor 2 Step
Action
Value(*)
Yes
No

1
Was the Powertrain On-Board Diagnostic (OBD) System Check performed?
--
Go to Step 2
Go to the Powertrain On Board Diagnostic (OBD) System Check

2
Engine at operating temperature.
Operate the engine above 1200 RPM for two minutes while monitoring HO2S 2 voltage on the scan tool.
Does the scan tool indicate HO2S 2 voltage varying outside the specified values?
425-475 mV
Go to Step 3
Go to Step 4

3
Turn ON the ignition switch.
Review and record scan tool Fail Records data and note parameters.
Operate the vehicle within Fail Records conditions as noted.
Using a scan tool, monitor Specific DTC info for DTC P0140 until the DTC P0140 test runs.
Does the scan tool indicate DTC failed this ignition?
--
Go to Step 4
Go to Diagnostic Aids

4
Turn ON the ignition switch.
Disconnect HO2S 2 and jumper the HO2S signal and low circuits (PCM side) to ground.
Using a scan tool, monitor HO2S 2 voltage.
Is HO2S 2 voltage less than the specified value?
150 mV
Go to Step 8
Go to Step 5

5
Remove the jumper wire from the HO2S signal circuit (leave the HO2S low circuit jumpered to ground).
Using a J 39200 Digital Multimeter, measure voltage between the HO2S 2 signal circuit (PCM side) and the HO2S 2 heater ground circuit.
Does HO2S 2 signal voltage measure near the specified value?
450 mV
Go to Step 6
Go to Step 7

6
Turn OFF the ignition switch.
Disconnect the PCM.
Check continuity of the HO2S 2 low circuit.
If the HO2S 2 low circuit measures over 5 ohms, repair open or poor connection as necessary. Refer to Heated Oxygen Sensor (O2S) Repair in Electrical Diagnosis.
Was a problem found?
--
Go to Step 13
Go to Step 9

7
Turn OFF the ignition switch
Disconnect the PCM.
Check continuity of the following circuits:
The HO2S 2 signal circuit between the PCM harness connector and the HO2S 2 harness connector.
The HO2S 2 low circuit between the PCM harness connector and the HO2S 2 harness connector.
If either circuit measures over 5 ohms, repair open or poor connection as necessary. Refer to Heated Oxygen Sensor (O2S) Repair in Electrical Diagnosis.
Was a problem found?
--
Go to Step 13
Go to Step 10

8
Check the following circuits for a poor terminal connection at the HO2S 2 harness connector:
HO2S 2 signal circuit.
HO2S 2 low circuit.
If a problem is found, replace terminal(*) as necessary. Refer to Heated Oxygen Sensor (O2S) Repair in Electrical Diagnosis.
Was a problem found?
--
Go to Step 13
Go to Step 11

9
Check for poor HO2S 2 low circuit terminal connection at the PCM.
If a problem is found, replace terminal as necessary. Refer to Heated Oxygen Sensor (O2S) Repair in Electrical Diagnosis.
Was a problem found?
--
Go to Step 13
Go to Step 12

10
Check the HO2S 2 signal circuit and the HO2S 2 low circuit for a poor terminal connection at the PCM.
If a problem is found, replace terminal(*) as necessary. Refer to Heated Oxygen Sensor (O2S) Repair in Electrical Diagnosis.
Was a problem found?
--
Go to Step 13
Go to Step 12

11
Replace HO2S 2. Refer to Heated Oxygen Sensor (HO2S) Replacement

Is action complete?
--
Go to Step 13
--

12
Replace the PCM.


Important
The replacement PCM must be programmed. Refer to PCM Replacement/Programming .


Is action complete?
--
Go to Step 13
--

13
Turn ON the ignition switch.
Review and record scan tool Fail Records data.
Clear DTCs.
Operate the vehicle within Fail Records conditions as noted.
Using a scan tool, monitor Specific DTC info for DTC P0140 until the DTC P0140 test runs.
Does the scan tool indicate DTC failed this ignition?

Tom_Sawyer_Man.. Thanks for those diagnostics flows. And i apologize for the one DTC, it should have read... P0141 O2 Sensor Heater Circuit Malfunction (Sensor 2). Right now I'm waiting to see if the actuator is stuck on the bypass valve/solenoid. And am still open to any thoughts comments on the problem. Thanks.

No worrys my friend. I just stumbled on the service manual info a couple weeks ago. Complete on all GM vehicles 1998 - 2005. and engine and trans... 98 -97. haven't figured out how to post off-line I-explorer pages to forum. therefore the diagrams do not show up. too bad pdf files are not valid.hope i have helped. Be sure you dont damage terminal connectors with probe tools.

Love all the diagnostics, but let'* put this in simplest terms.



If you aren't getting boost, you need to rule out the obvious before looking for the obscure. Check the following:

1. Is there good tension on the */c belt, and is the belt in good condition (no slippage)?
2. Do you hear any nasty noises coming out of the */c (loose marbles)?
3. Remove the boost control actuator (BCA) rod from the butterfly valve arm on the throttle body, and check for free rotation of the butterfly valve pivot rod. If there is any binding spray lubricant (WD40) where the pivot rod enters and exits the throttle body (front and back) and work it until it moves with no restrictions.
4. Hook the BCA rod back up. Unhook the vaccum source line from the boost control solenoid (BCS) and hook the vacuum source directly to the top of the BCA at the vaccum port. Check for BCA movement as follows. Engine off, arm fully retracted (full boost position). Engine on at idle, arm fully extended (zero boost position). Give the throttle a shot and observe the arm move from extended to retracted. Take the car for a short ride and try a couple of WOT'*. With this hook up you should have full boost. DO NOT LEAVE IT SET UP THIS WAY OTHER THAN A VERY SHORT TEST DRIVE. If the BCA moves as described, replace the BCS. If the BCA does not move as described, replace the BCA.

The primary suspects are a binding butterfly valve pivot rod, faulty BCS, and faulty BCA. My bet is the problem will be a faulty BCS.

Here is a thread that describes this further:
https://www.gmforum.com/trouble-shooting-test-procedures-141/boost-control-actuator-284309/

That'* a good either/or test for the BCA and BCS. He checked the usual suspects on the drive side. After i finally got the MAP/MAF readings, it was clear to me there was no boost. Up till then, others working on it were focusing on fuel and all kinds of other areas. I just wanted the MAP/MAF readings And I wouldn't be surprised, if he does have a complicating, but different, problem with 1 or both o2 sensors.The sensors are 14 years old and were stored in a damp, dank barn for 7 months with the car. Do ya think they might be up way past their bedtime?

Thanks.

Do a scan on them, no signal is about 440mv. After going in to can't remember if it'* open or closed loop,it should start going up and down after 20 seconds or so, or when up to temp.