What can cause my 2008 jeep commander 4.7l V8 to feel sluggish when accelerating? I've changed the plugs, egr valve, map sensor, air filter, pcv valve and oil. I started to notice it after my catalytic converter and oxygen sensor were replaced by the dealer as they were found defective. Any suggestions?

Hi there:

DTC P0401 - Insufficient EGR Flow
EGR stands for Exhaust Gas Recirculation. It is part of the vehicle emmissions system, and is used to reduce combustion temperature and pressure to control Oxides of Nitrogen. There are generally three parts to the EGR system: the EGR valve, an actuator solenoid, and a differential pressure sensor EGR (DPFE). These things work together to deliver the correct amount of recirculation based on engine temperature, load, etc. The P0401 code means that OBD detected an insufficient amount of EGR.



A code P0401 most likely means one or more of the following has happened:
The DPFE (differential pressure feedback EGR) sensor is faulty and needs to be replaced
There is a blockage in the EGR (tube), most likely carbon buildup
The EGR valve is faulty
The EGR valve may not be opening due to a lack of vaccuum


Possible Solutions:
In fixing this code, it is quite common for people to just replace the EGR valve only to have the OBD code return. The EGR valve is not always the culprit.


Use a vacuum pump and pull the EGR valve open while monitoring engine RPM's & DPFE voltage. There should be a noticable difference in RPM's with the EGR open
Clean out the EGR valve and/or tubing to remove deposits
Check the voltage at the DPFE, compare to specified values (refer to a repair manual for your specific model)
Replace the DPFE sensor (with a good quality / OEM one)
Replace the EGR valve





DTC P0106 - MAP/Barometric Pressure Circuit Range/Performance Problem
The Powertrain Control Module (PCM) uses the Manifold Absolute Pressure Sensor (MAP) to monitor engine load. (NOTE: Some vehicles have a Barometric Pressure (BARO) sensor that is integral to the Mass Air Flow (MAF) sensor and do not have a MAP sensor. Other vehicles have a MAF/BARO and a redundant MAP sensor where the MAP sensor functions as a backup input in case of MAF failure.) The PCM supplies a 5 Volt reference signal to the MAP sensor. Usually the PCM also supplies a ground circuit to the MAP sensor as well. As the manifold pressure changes with load, the MAP sensor input informs the PCM. At idle the voltage should be 1 to 1.5 Volts and approximately 4.5 Volts at Wide Open Throttle (WOT). The PCM looks for any change in manifold pressure to be preceded by a change in engine load in the form of changes in throttle angle, engine speed, or Exhaust Gas Recirculation (EGR) flow. If the PCM doesn't see any of these factors change while detecting a rapid change in MAP value, it will set a P0106.


A P0106 could be caused by:
Bad MAP sensor
Water/dirt intrusion affecting MAP sensor connector
Intermittent open in the reference, ground, or signal wire for the MAP sensor
Intermittent short in the reference, ground, or signal wire for the MAP sensor
Ground problem due to corrosion causing intermittent signal problem
A break in the flexible air intake duct between the MAF and the intake manifold
Bad PCM (do not assume the PCM is bad until you've exhausted all other possibilities)

Possible Solutions: Using a scan tool, watch the MAP sensor value with the key on, engine off. Compare the BARO reading with the MAP reading. They should be roughly equal. The voltage for the MAP sensor should read approx. 4.5 volts. Now start the engine and look for a significant drop in the MAP sensor voltage indicating the MAP sensor is working.

If the MAP reading doesn't change perform the following:

With the Key on, engine off, disconnect the vacuum hose from the MAP sensor. Using a vacuum pump, pull 20 in. of vacuum on the MAP sensor. Does the voltage drop? It should. If it doesn't inspect the MAP sensor vacuum port and vacuum hose to manifold for a restriction of some kind. Repair or replace as necessary.
If there are no restrictions, and the value doesn't change with vacuum, then perform the following: with the Key on and engine off and the MAP sensor unplugged, check for 5 Volts at the reference wire to the MAP sensor connector with a Digital Voltmeter. If there is none, check for reference voltage at the PCM connector. If the reference voltage is present at the PCM connector but not the MAP connector, check for open or short in the reference wire between MAP and PCM and retest.
If reference voltage is present, then check for existing ground at the MAP sensor connector. If it isn't present then repair open/short in the ground circuit.
If ground is present, then replace MAP sensor.


DTC P0171 - System Too Lean (Bank 1)
Basically this means that an oxygen sensor in bank 1 has detected a lean condition (too much oxygen in the exhaust). On V6/V8/V10 engines, Bank 1 is the side of the engine that has cylinder #1. The P0171 is one of the more common trouble codes.



This code is triggered by the first downstream (front) O2 sensor. The sensor provides a reading of the air:fuel ratio leaving the engine's cylinders, and the vehicles powertrain/engine control module (PCM/ECM) uses that reading and adjusts to keep the engine running at that optimum ratio of 14.7:1. If something is not right and the PCM cannot maintain the 14.7:1 ratio, but rather there is too much air, it triggers this code.


You'll want to also read our article on short and long term fuel trims to help understand the operation of the engine. Note: This DTC is very similar to P0174, and in fact your vehicle may show both codes at the same time.


A code P0171 may mean that one or more of the following has happened:
The MAF (Mass Air Flow) Sensor is dirty or faulty
Note: The use of "oiled" air filters may cause the MAF to become dirty if the filter is over-oiled. There is also an issue with some vehicles where the MAF sensors leak the silicone potting material used to protect the circuitry.
There could be a vacuum leak downstream of the MAF sensor
Possible cracked vacuum or PCV line/connection
Faulty or stuck open PCV valve
Failed or faulty oxygen sensor (bank 1, sensor 1)
Sticking/plugged or failed fuel injector
Low fuel pressure (possible plugged/dirty fuel filter!)
Exhaust leak between engine and first oxygen sensor


Possible Solutions: A lot of times, cleaning the MAF sensor and finding/fixing vacuum leaks fix the problem. If you're on a tight budget, start there, but that may not be the fix for certain. So, possible solutions include:


Clean the MAF sensor. Consult your service manual for it's location if you need help. I find it's best to take it off and spray it with electronics cleaner or brake cleaner. Make sure you are careful not to damage the MAF sensor, and make sure it's dry before reinstalling
Inspect all vacuum and PCV hoses, replace/repair as required
Inspect all hoses and connections in the air intake system
Inspect and/or test the intake manifold gaskets for leakage
Check for a dirty fuel filter and proper fuel pressure
Ideally you'll want to monitor short and long term fuel trims using an advanced scan tool
If you have access, you may want to run a smoke test




DTC P1170 - HO2S Bank 1 Sensor 1 Circuit Fixed (Bank 1 Sensor 1)

Most likelly cause is Aging Heated Oxygen Sensor 1/1 Front RH. Hook up a Scantool and monitor sensor responce. You can also check resistance of Heater on terminal D and C for about 6ohms.

As usual check for any vacuum/exhaust leaks. Maybe check fuel pressure and fuel filter.





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Before you replace the injectors have them do an injector balance test. Normally wet weather does not effect fuel system. Sounds more like you have a crank or cam sensor acting up.

Great to hear.

Try a few if these ideas...

Priority Action Part Type Cause
1 Inspect Spark Plug Fouled, Damaged, or Broken Spark Plug(s).
2 Inspect Hose (PCV) Clogged or Collapsed PCV Hoses.
3 Inspect Wireset Worn, Damaged or Faulty Spark Plug Wire(s).
4 Inspect Distributor Worn, Damaged or Faulty Distributor.
5 Inspect Catalytic Converter Clogged or Faulty Catalytic Converter.
6 Inspect Fuel Pump Low Fuel Pressure.
7 Inspect TimingSet Slipped TimingChain or Worn TimingGear(s).
8 Inspect Knock Sensor Improperly Connected or Faulty Knock Sensor.
9 Inspect M.A.P. (Manifold Absolute Pressure) Sensor Faulty M.A.P. Sensor.
10 Inspect Throttle Position Sensor Faulty or Incorrectly Connected Throttle Position Sensor.
11 Inspect Mass Air Flow (MAF) Sensor Damaged, Loose, or Faulty Mass Air Flow Sensor or Circuit.
12 Inspect Air Cleaner Temperature Sensor Damaged or Faulty Air Cleaner Tempature Sensor.
13 Inspect Fuel Injector Pressure Regulator Faulty Fuel Injector Pressure Regulator.
14 Inspect Piston Ring Set Worn or Broken Piston Rings.
15 Inspect Timing Specification Incorrect Ignition Timing.
16 Inspect Fuel System Pressure Incorrect Fuel Pressure Being Delivered to Carburetor or Fuel Injection System.
17 Inspect Fuel Filter Clogged or Dirty Fuel Filter.
18 Inspect PCV Valve Plugged or Damaged PCV Valve.
19 Inspect Valve Burned, Worn, or Sticking Exhaust Valves.
20 check idle stop solenoid - if faulty, could cause rough idling
21 inspect distributor cap/rotor - if burnt, could cause loss of acceleration

P0401- Exhaust Gas Recirculation Flow Insufficient Dectected
Possible causes - Harness or connectors (EGR volume control valve circuit is open or shorted.)
- EGR volume control valve stuck closed
- EGR volume control solenoid valve
- Dead (Weak) battery
- EGR passage clogged
- Exhaust gas leaks Possible solution - Clean EGR Valve
- Repair EGR harness or connector
- Replaced EGR volume control solenoid valve
- Replaced EGR volume control valve
Code P0171- Fuel Injection System Too Lean Bank 1 Possible causes - Intake air leaks
- Front Heated oxygen sensor may be faulty
- Injectors may be faulty
- Exhaust gas leaks
- Incorrect fuel pressure
- Lack of fuel
- Mass air flow sensor may be faulty
- Incorrect PCV hose connection Possible solution Dirty air filter of faulty air flow sensor are common causes of the problem P0174- Fuel Injection System Too Lean Bank 2 Possible causes - Intake air leaks
- Front Heated oxygen sensor may be faulty
- Injectors may be faulty
- Exhaust gas leaks
- Incorrect fuel pressure
- Lack of fuel
- Mass air flow sensor may be faulty
- Incorrect PCV hose connection Possible solution Dirty air filter of faulty air flow sensor are common causes of the problem.

1) dirty air filter

2) vacuum leak

3) false reading from mass air flow sensor

4) false reading from coolant temperature sensor

5) improper tires inflation

6) topping off gas when fill-up (soaking emission lines with fuel)

7) Positive Crankcase Ventilation (PCV) and breather element clogging

8) Exhaust Gas Recirculation(EGR) Valve stuck with carbon and EGR passage tube is block with carbon.

9) low or dirty transmission fluid + filter (if it's an automatic)

10) excessive load

Maf or map sensor is bad or egr stuck open.

1 Inspect M.A.P. Sensor Faulty M.A.P. Sensor. 2 Inspect EGR Valve Improperly Functioning or Faulty EGR Valve. 3 Inspect Fuel Injector Dirty or Worn Fuel Injectors. 4 Inspect Idle Air Control Valve Damaged, Loose, or Faulty Idle Air Control Valve. 5 Inspect Idle Speed Actuator Damaged, Loose, or Faulty Idle Speed Actuator. 6 Inspect Throttle Position Sensor Faulty or Incorrectly Connected Throttle Position Sensor. 7 Inspect Fuel Filter Clogged or Dirty Fuel Filter. 8 Inspect PCV Valve Plugged or Damaged PCV Valve. 9 Inspect Carburetor Worn, Faulty or Damaged Carburetor. 10 Inspect Valve Burned, Worn, or Sticking Exhaust Valves. 12 Inspect TimingSet Slipped TimingChain or Worn TimingGear(s). 13 Inspect Fuel Pump Faulty Fuel Pump. 14 Inspect Camshaft Camshaft Lobes Worn. 16 Inspect Point Set Burned, Worn or Incorrectly Set Ignition Points.

Try replacing the coolant temperature sensor for the injection system.