Page 4897 of 6000

6E–240
ENGINE DRIVEABILITY AND EMISSIONS
Diagnostic Trouble Code (DTC) P0601 PCM Memory
Circuit Description
The powertrain control module (PCM) used in this vehicle
utilizes an electrically erasable programmable read-only
memory (EEPROM). The EEPROM contains program
information and the calibrations required for engine,
transmission, and powertrain diagnostics operation.
Unlike the PROM used in past applications, the EEPROM
is not replaceable.
Conditions for Setting the DTC
The PCM detects an internal program fault (check sum
error).
Action Taken When the DTC Sets
The PCM will not illuminate the malfunction indicator
lamp (MIL).
The PCM will store conditions which were present
when the DTC was set in the Failure Records data only.
Conditions for Clearing the MIL/DTC
DTC P0601 can be cleared by using the Tech 2 “Clear
Info” function or by disconnecting the PCM battery
feed.
Diagnostic Aids
DTC P0601 indicates that the contents of the
EEPROM have changed since the PCM was
programmed. The only possible repair is PCM
replacement.
DTC P0601 – PCM Memory
StepActionVa l u e ( s )Ye sNo
1Was the “On-Board Diagnostic (OBD) System Check”
performed?
—Go to Step 2
Go to OBD
System
Check
2Replace the PCM.
IMPORTANT:The replacement PCM must be
programmed. Refer to
UBS 98model year Immobilizer
Workshop Manual.
Is the action complete?—Verify repair—
Page 4898 of 6000

6E–241 ENGINE DRIVEABILITY AND EMISSIONS
Diagnostic Trouble Code (DTC) P1154 HO2S Circuit Transition Time Ratio
Bank 2 Sensor 1
060RW190
Circuit Description
The powertrain control module (PCM) monitors the
heated oxygen sensor (HO2S) activity for 90 seconds
after “closed loop” and stoichiometric operation have
been enabled. During the monitor period the PCM counts
the number of times that the HO2S responds from
rich-to-lean and from lean-to-rich and adds the amount of
time it took to complete all transitions. With this
information, an average time for all transitions can be
determined. The PCM then divides the rich-to-lean
average by the lean-to-rich average to obtain a ratio. If
the HO2S transition time ratio is not within this range,
DTC P1154 will be set, indicating that the oxygen sensor
is not responding as expected to changes in exhaust
oxygen content.
Conditions for Setting the DTC
No related DTCs.
Engine coolant temperature (ETC) is above 50C
(122F) for automatic transmission; 75C (167F) for
manual transmission.
The engine is operating in “closed loop.”
The engine has been running at least one minute.
Canister purge duty cycle is greater than 2%.
Engine speed is between 1500 RPM and 3000 RPM.
Mass air flow is between 9 g/second and 42 g/second.
Above conditions are present for a 3-second
monitoring period.
90 seconds after “closed loop” and stoichiometric
operation have been enabled, Bank 2 HO2S 1
transition ratio between lean to rich and rich to lean is
less than 0.44 or greater than 3.8.
Action Taken When the DTC Sets
The PCM will illuminate the malfunction indicator lamp
(MIL) after the second consecutive trip in which the
fault is detected.
”Open loop” fuel control will be in effect.
The PCM will store conditions which were present
when the DTC was set as Freeze Frame and in the
Failure Records data.
Conditions for Clearing the MIL/DTC
DTC P1154 can be cleared by using Tech 2 “Clear Info”
function or by disconnecting the PCM battery feed.
Diagnostic Aids
A multifunction in the HO2S heater ignition feed or ground
circuit may cause a DTC P1154 to set. Check HO2S
heater circuitry for intermittent faults or poor connections.
If connections and wiring are OK and DTC P1154
continues to set, replace the Bank 2 HO2S 1.
Reviewing the Failure Records vehicle mileage since the
diagnostic test last failed may help determine how often
Page 4899 of 6000

6E–242
ENGINE DRIVEABILITY AND EMISSIONS
the condition that caused the DTC to be set occurs. This
may assist in diagnosing the condition.
Test Description
Number(s) below refer to the step number(s) on the
Diagnostic Chart.
3. A condition that affects other heated oxygen sensors
indicates probable contamination. To avoid
damaging replacement sensors, correct the
condition which caused the contamination before
replacing the affected sensors.5. This step checks for conditions which may cause the
heated oxygen sensor to appear faulty. Correct any
of the described conditions if present.
8. To avoid damaging replacement sensors, correct the
condition which caused the contamination before
replacing the affected sensors.
DTC P1154 – HO2S Transition Time Ratio Bank 2 Sensor 1
StepActionVa l u e ( s )Ye sNo
1Was the “On-Board Diagnostic (OBD) System Check”
performed?
—Go to Step 2
Go to OBD
System
Check
2IMPORTANT:If any other DTCs are set (except P1133
and/or P1134), refer to those DTCs before proceeding
with this diagnostic chart.
1. Idle the engine at operating temperature.
2. Operate the vehicle within parameters specified
under “Conditions for Setting the DTC” criteria
included in Diagnostic Support.
3. Using a Tech 2, monitor “Specific DTC” info for DTC
P1154 until the DTC P1154 test runs.
Note the test result.
Does Tech 2 indicate DTC failed this ignition?
—Go to Step 3
Refer to
Diagnostic
Aids
3Did Tech 2 also indicate P1133, and/or P1134 test
failed?
—Go to Step 17Go to Step 4
4Check for leaks at the pipe joints.
Are the joints leaking?
—Go to Step 5Go to Step 6
5Tighten the U-bolt nuts at the leaking joints.
Is your action complete?
—Go to Step 2—
6Check for gaskets that are damaged or improperly
installed.
Are there damaged or misaligned gaskets?
—Go to Step 7Go to Step 8
71. Replace the damaged gaskets.
2. Align the connections.
3. Tighten the connections.
Is your action complete?
—Go to Step 2—
8Check for loose exhaust flange connections.
Are the flange connections loose?
—Go to Step 9Go to Step 10
9Tighten the stud nuts or bolts to specifications.
Is your action complete?
—Go to Step 2—
10Check for burned or corroded exhaust pipes.
Are the exhaust pipes burned or corroded?
—Go to Step 11Go to Step 12
11Replace the exhaust pipes, as required.
Is your action complete?
—Go to Step 2—
Page 4900 of 6000

6E–243 ENGINE DRIVEABILITY AND EMISSIONS
DTC P1154 – HO2S Transition Time Ratio Bank 2 Sensor 1
StepNo Ye s Va l u e ( s ) Action
12Check for leaks at the exhaust manifold.
Are there leaks at the exhaust manifold?
—Go to Step 13Go to Step 14
13Tighten the bolts to specifications or replace the
manifold if necessary.
Is your action complete?
—Go to Step 2—
14Visually/physically inspect the following items:
Ensure that the Bank 2 HO2S 1 is securely
installed.
Check for corrosion on terminals.
Check terminal tension (at Bank 2 HO2S 1 and at
the PCM).
Check for damaged wiring.
Was a problem found in any of the above areas?
—Go to Step 18Go to Step 15
151. Disconnect Bank 1 HO2S 1.
2. Ignition “ON.”
3. Using a DVM at the PCM side of the HO2S 1
connector, measure the voltage between the high
signal circuit and ground.
Also measure the voltage between the low signal
circuit and ground.
Are both voltages in the specified range?
3-4 V
Go to Step
16
Go to Step 19
161. With Bank 1 HO2S 1 disconnected, jumper the high
and low (PCM side) signal circuits to ground.
2. Ignition “ON.”
3. Using Tech 2, monitor the Bank 2 HO2S 1 voltage.
Does the scan too indicate less than 10 mV and
immediately return to about 450 mV when the jumper is
removed?
—Go to Step 21Go to Step 22
17Replace affected heated oxygen sensors.
NOTE: Before replacing sensors, the cause of the
contamination must be determined and corrected.
Fuel contamination.
Use of improper RTV sealant.
Engine oil/coolant consumption.
Is the action complete?
—Verify repair—
18Repair condition as necessary.
Is the action complete?
—Verify repair—
19Check for faulty PCM connections or terminal damage.
Is the action complete?
—Verify repairGo to Step 20
20Repair open, short or grounded signal circuit.
Is the action complete?
—Verify repair—
Page 4901 of 6000
6E–244
ENGINE DRIVEABILITY AND EMISSIONS
DTC P1154 – HO2S Transition Time Ratio Bank 2 Sensor 1
StepNo Ye s Va l u e ( s ) Action
21Replace Bank 2 HO2S 1.
Is the action complete?
—Verify repair—
22Replace the PCM.
IMPORTANT:The replacement PCM must be
programmed. Refer to
UBS 98model year Immobilizer
Workshop Manual.
Is the action complete?—Verify repair—
Page 4902 of 6000

6E–245 ENGINE DRIVEABILITY AND EMISSIONS
Diagnostic Trouble Code (DTC) P1171 Fuel System Lean During Acceleration
060RW193–1
Circuit Description
The powertrain control module (PCM) internal circuitry
can identify if the vehicle fuel system is capable of
supplying adequate amounts of fuel during heavy
acceleration (power enrichment). The PCM monitors the
voltage of the oxygen sensor during power enrichment.
When a power enrichment mode of operation is
requested during “closed loop” operation (by heavy
acceleration), the PCM will provide more fuel to the
engine. Under these conditions the PCM should detect a
“rich” condition (high oxygen sensor voltage). If this “rich”
exhaust is not detected at this time, a DTC P1171 will set.
A plugged fuel filter, restricted fuel line, restricted in-tank
filter or defective fuel pump can prevent adequate
amounts of fuel from being supplied during power
enrichment mode.
Conditions for Setting the DTC
No related DTCs.
Engine is operating in “closed loop power enrichment”
mode for 3 seconds.
Engine coolant temperature is above 60C (140F).
While in “power enrichment” mode the oxygen sensor
voltage remains below 400 mV for 3 seconds.
Action Taken When the DTC Sets
The PCM will illuminate the malfunction indicator lamp
(MIL) the first the fault is detected.
The PCM will store conditions which were present
when the DTC was set as Freeze Frame and in the
Failure Records data.
Conditions for Clearing the MIL/DTC
DTC P1171 can be cleared by using Tech 2 “Clear Info”
function or by disconnecting the PCM battery feed.
Diagnostic Aids
A restricted fuel filter or fuel line, restricted in-tank filter,
or a defective fuel pomp may supply adequate
Page 4903 of 6000

6E–246
ENGINE DRIVEABILITY AND EMISSIONS
amounts of fuel at idle, but may not be able to supply
enough fuel during heavy acceleration.
Water or alcohol in the fuel may cause low HO2S
voltage during acceleration.
Check for faulty or plugged fuel injector(s).
Check for low fuel.
Test Description
Number(s) below refer to the step number(s) on the
Diagnostic Chart.4. When the engine is idling or at steady cruise, the
HO2S voltage should vary from between
approximately 100 mV to 900 mV. It is possible to
measure a satisfactory fuel pressure at idle even
though the pressure may drop at high flow
requirements. It may be necessary to watch fuel
pressure at high engine load.
5. Wrap a shop towel around the fuel pressure
connector to absorb any small amount of fuel
leakage that may occur when installing gauge.
Ignition “ON,” pump pressure should be 280-320
kPa.
DTC P1171 – Fuel System Lean During Acceleration
StepActionVa l u e ( s )Ye sNo
1Was the “On-Board Diagnostic (OBD) System Check”
performed?
—Go to Step 2
Go to OBD
System
Check
2Are any component-related DTCs set?
—
Go to
component
DTC charts
Go to Step 3
31. Check the vehicle’s fuel tank for an adequate
amount of fuel.
2. Add fuel to the vehicle’s fuel tank if the tank is almost
empty.
Was fuel added to the vehicle’s fuel tank?
—Go to Step 4Go to Step 5
41. Place the transmission in park.
2. Using Tech 2, observe HO2S 1 voltage while
running warm engine 75
C-95C (167F-203F) at
1200 RPM.
3. HO2S 1 voltage should vary within the specified
range.
4. Quickly open the throttle halfway for a few seconds.
Did the voltage suddenly rise toward the high end of the
specified range?
100-900 mV
Go to Chart
A-7
Go to Step 5
51. Disconnect the fuel pump relay and crank the
engine to relieve the fuel pressure.
2. Install the fuel pressure gauge.
3. Start the engine and idle at normal operating
temperature.
4. Disconnect the vacuum line going to the fuel
pressure regulator.
With the engine running, is the fuel pressure within the
specified range?
280-325 kPa
(41-46 psi)
Go to OBD
System
Check
Go to Step 6
6Check for restricted fuel lines or restricted in-line filter.
Was a problem found?
—Verify repairGo to Step 7
Page 4904 of 6000
6E–247 ENGINE DRIVEABILITY AND EMISSIONS
DTC P1171 – Fuel System Lean During Acceleration
StepNo Ye s Va l u e ( s ) Action
71. Ignition “OFF.”
2. Remove the fuel pump relay and replace it with a
fused jumper which will connect the relay’s battery
terminal to the terminal leading to the fuel pump
fuse.
3. While the fuel pump is operating, use pliers to slowly
close the return line (do not exceed the first
specified value).
Using the pliers to restrict the return line, can the fuel
pressure be manipulated to exceed the second
specified value?
414 kPa
(60 psi)
325 kPa
(46 psi)
Go to
Diagnostic
Aids
Go to Step 8
8Check for:
Faulty fuel pump
Restricted fuel pump strainer (sock)
Incorrect fuel pump
Incorrect fuel being used
Hot fuel
Is the action complete?
—Verify repair—