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Hummer H2. Manual - part 1557

1. Turn OFF the engine.

2. Disconnect the respective ignition coil.

3. Start the engine.

4. Measure the frequency at the IC circuit with

the DMM set to DC Hertz. Refer to
Measuring Frequency in Wiring Systems.

Is the frequency within the specified range?

3-20

Go to Step 7

Go to Step 4

Measure the voltage from the IC circuit of the
ignition coil to a good ground with the DMM.
Is the voltage more than the specified value?

1 V

Go to Step 13

Go to Step 5

1. Turn OFF the ignition.

2. Disconnect the PCM connector.

3. Test the IC circuit between the ignition coil

connector and the PCM connector for
continuity with the DMM.

Does the DMM indicate continuity?

Go to Step 6

Go to Step 14

Test the respective IC circuit for a short to ground.
Refer to Testing for Short to Ground in Wiring
Systems.
Did you find and correct the condition?

Go to Step 17

Go to Step 10

1. Turn ON the ignition, with the engine OFF.

2. Probe the ignition 1 voltage circuit of the

ignition coil with a test lamp that is connected
to battery ground. Refer to Troubleshooting
with a Test Lamp in Wiring Systems.

Does the test lamp illuminate?

Go to Step 8

Go to Step 11

Probe the ground circuit of the ignition coil with a
test lamp connected to battery voltage. Refer to
Troubleshooting with a Test Lamp in Wiring
Systems.
Does the test lamp illuminate?

Go to Step 9

Go to Step 12

Test for an intermittent and for a poor connection at
the ignition coil. Refer to Testing for Intermittent
Conditions and Poor Connections and Connector
Repairs in Wiring Systems.
Did you find and correct the condition?

Go to Step 17

Go to Step 15

Test for an intermittent and for a poor connection at
the PCM. Refer to Testing for Intermittent
Conditions and Poor Connections and Connector
Repairs in Wiring Systems.

2004 Hummer H2

2004 ENGINE PERFORMANCE Engine Controls Diagnosis (DTC P0171/P0174 To DTC P0507 (TAC)) - 4.8L, 5.3L, and

6.0L - Hummer H2

DTC P0420 OR P0430

Circuit Description

The three-way catalytic converter (TWC) reduces emissions of hydrocarbons (HC), carbon monoxide (CO), and
oxides of nitrogen (NOx). The catalyst within the converter promotes a chemical reaction, which oxidizes the
HC and CO that are present in the exhaust gas. This process converts these chemicals into water vapor and
carbon dioxide (CO2), and will reduce the NOx, by converting them into nitrogen. The catalytic converter also
stores oxygen. The powertrain control module (PCM) monitors this process using heated oxygen sensor (HO2S)
bank 1 sensor 2 and HO2S bank 2 sensor 2, located in the exhaust stream after the TWC. These sensors are
referred to as the catalyst monitor sensors. The catalyst monitor sensors produce an output signal the PCM uses

Did you find and correct the condition?

Go to Step 17

Go to Step 16

Repair the open in the ignition 1 voltage circuit.
Refer to Wiring Repairs in Wiring Systems.
Did you complete the repair?

Go to Step 17

Repair the open in the ground circuit for the ignition
coil. Refer to Wiring Repairs in Wiring Systems.
Did you complete the repair?

Go to Step 17

Repair the IC circuit for a short to voltage. Refer to
Wiring Repairs in Wiring Systems.
Did you complete the repair?

Go to Step 17

Repair open in the IC circuit. Refer to Wiring
Repairs in Wiring Systems.
Did you complete the repair?

Go to Step 17

Replace the ignition coil. Refer to Ignition Coil(s)
Replacement .
Did you complete the replacement?

Go to Step 17

Replace the PCM. Refer to Powertrain Control
Module (PCM) Replacement .
Did you complete the replacement?

Go to Step 17

1. Clear the DTCs with a scan tool.

2. Turn OFF the ignition for 30 seconds.

3. Start the engine.

4. Operate the vehicle within the Conditions for

Running the DTC. You may also operate the
vehicle within the conditions that you
observed from the Freeze Frame/Failure
Records.

Did the DTC fail this ignition?

Go to Step 2

Go to Step 18

Observe the Capture Info with a scan tool.
Are there any DTCs that have not been diagnosed?

Go to

Diagnostic

Trouble Code

(DTC) List

System OK

2004 Hummer H2

2004 ENGINE PERFORMANCE Engine Controls Diagnosis (DTC P0171/P0174 To DTC P0507 (TAC)) - 4.8L, 5.3L, and

6.0L - Hummer H2

to indicate the oxygen storage capacity of the catalyst. This determines the catalysts ability to effectively
convert the exhaust emissions.

If the catalyst is functioning correctly, the HO2S bank 1 sensor 2 and HO2S bank 2 sensor 2 signals will be far
less active than the signals that are produced by HO2S bank 1 sensor 1 and HO2S bank 2 sensor 1. This
indicates that the TWC oxygen storage capacity is at an acceptable threshold. When the response time of the
catalyst monitor sensors are close to that of the fuel control sensors, the ability of the catalyst to store oxygen
may be below an acceptable threshold.

The PCM performs this diagnostic test at idle. When the conditions for running this DTC are met, the following
occurs:

The air-to-fuel ratio transitions from lean to rich.

The air-to-fuel ratio transitions from rich to lean, opposite the first air-to-fuel ratio transition.

The PCM captures the response time of the front and the rear HO2S when the air-to-fuel ratio transitions
occur. The HO2S response time changes from less than 350 mV to more than 600 mV, and from more
than 600 mV to less than 350 mV.

The PCM measures the time necessary for the rear HO2S voltage to cross a reference lean-to-rich
threshold, and the time necessary for the front HO2S voltage to cross the same lean-to-rich threshold. The
difference between the front HO2S time and the rear HO2S time indicates the oxygen storage capacity of
the catalyst. If the PCM detects that this time difference is less than a predetermined value, DTC P0420
for bank 1 or DTC P0430 for bank 2 sets.

Conditions for Running the DTC

DTCs P0068, P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0120, P0125,
P0128, P0131, P0132, P0133, P0134, P0135, P0136, P0137, P0138, P0140, P0141, P0151, P0152,
P0153, P0154, P0155, P0156, P0157, P0158, P0160, P0161, P0171, P0172, P0174, P0175, P0200,
P0220, P0300, P0325, P0327, P0332, P0335, P0336, P0341, P0342, P0343, P0351-P0358, P0442, P0443,
P0446, P0449, P0452, P0453, P0455, P0496, P0502, P0503, P0506, P0507, P1125, P1133, P1134,
P1153, P1154, P1516, P2101, P2108, P2120, P2121, P2125, P2135 are not set.

The engine has been running for more than 10 minutes.

The intake air temperature (IAT) is between -7 to +85°C (+20 and +185°F).

The barometric pressure (BARO) is more than 75 kPa.

The engine coolant temperature (ECT) is more than 70-120°C (158-248°F).

Since the end of the last idle period, the engine speed has been more than 900 RPM for 46 seconds.

The engine must be at a stable idle speed, within 200 RPM of desired idle.

The battery voltage is more than 10.7 volts.

The Closed Loop fuel control is enabled.

Conditions for Setting the DTC

The PCM determines that the oxygen storage capability of the TWC has degraded to less than a calibrated
threshold.

2004 Hummer H2

2004 ENGINE PERFORMANCE Engine Controls Diagnosis (DTC P0171/P0174 To DTC P0507 (TAC)) - 4.8L, 5.3L, and

6.0L - Hummer H2

Action Taken When the DTC Sets

The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.

The control module records the operating conditions at the time the diagnostic fails. The control module
stores this information in the Freeze Frame/Failure Records.

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

The catalyst test may abort due to a change in the engine load. Do not change the engine load, ensure the
AC is OFF, the coolant fan is not cycling, while a catalyst test is in progress.

Driving the vehicle under the conditions outlined in the Inspection/Maintenance (I/M) section can verify
whether the fault is present.

These conditions may cause a catalytic converter to degrade. Inspect for the following conditions:

{

An engine misfire

{

High engine oil or high coolant consumption

{

Retarded spark timing

{

A weak or poor spark

{

A lean fuel mixture

{

A rich fuel mixture

{

A damaged oxygen sensor or wiring harness.

{

If an intermittent condition cannot be duplicated, the information included in Freeze Frame data
can be useful in determining the vehicle operating conditions when the DTC was set.

The catalyst may have been temporarily contaminated with a chemical from a fuel additive, fuel
contamination or any of the above conditions.

If the condition is determined to be intermittent, refer to Intermittent Conditions .

Test Description

The numbers below refer to the step numbers on the diagnostic table.

5: A catalytic converter which has been discolored may be due to an engine running rich, lean or had a
previous misfire. Verifying the fuel trim percentages may be of assistance in determining if such a
condition exists.

2004 Hummer H2

2004 ENGINE PERFORMANCE Engine Controls Diagnosis (DTC P0171/P0174 To DTC P0507 (TAC)) - 4.8L, 5.3L, and

6.0L - Hummer H2

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