2007 Malibu MAXX Multiple Fault Codes

 Ok, they dropped off this 2007 Malibu. Complaints were stalling, low power, MIL, Reduced Power message, etc. When I went to drive the car into the shop it was doing all of the above so it seemed like a good time to look at codes and data. 

Engine P0106 | Manifold Absolute Pressure (MAP) Sensor Performance (Symptom 00) - Test Failed Since DTC Clear, Test Not Passed Since Power Up. 

P0107 | Manifold Absolute Pressure (MAP) Sensor Circuit Low Voltage (Symptom 00) - Current DTC, Test Failed Since DTC Clear, History DTC, Test Not Passed Since Power Up, Current DTC Since Power Up, Warning Indicator Requested. 

P0452 | Fuel Tank Pressure (FTP) Sensor Circuit Low Voltage (Symptom 00) - Current DTC, Test Failed Since DTC Clear, History DTC, Test Not Passed Since Power Up, Current DTC Since Power Up, Warning Indicator Requested. 

P0522 | Engine Oil Pressure (EOP) Sensor Circuit Low Voltage (Symptom 00) - Current DTC, Test Failed Since DTC Clear, History DTC, Test Not Passed Since Power Up, Current DTC Since Power Up. 

P0532 | Air Conditioning (A/C) Refrigerant Pressure Sensor Circuit Low Voltage (Symptom 00) - Current DTC, Test Failed Since DTC Clear, History DTC, Current DTC Since Power Up. 

P0641 | 5 Volt Reference 1 Circuit (Symptom 00) - Current DTC, Test Failed Since DTC Clear, History DTC, Test Not Passed Since Power Up, Current DTC Since Power Up, Warning Indicator Requested

A look at the scan data showed no MAP, FTP, Oil Pressure or A/C voltage from those sensors. Now what all those sensors have in common is they share a 5 volt reference circuit to be operable. The most likely possibilities here are that, (A) the engine computer is not outputting a reference voltage, (B) one of the sensors is shorting the reference voltage to ground, (C) the reference voltage circuit wiring is being shorted to ground at some point in the harness. The P0641 would set in any of those conditions. Now it was time to close shop, start here in the morning.

The next morning the car started and ran perfectly fine. Other than the MIL still on you would not know it had a problem. All of the previously dead sensors were now outputting voltage signals. My plan of attack was already decided though and this newest development wasn't changing it much. I would look at the harness and connectors as near each of the affected sensors as I could reasonably access. I didn't want to start by doing a lot of work, unless that became necessary. For instance, to gain unfettered access to some of the sensors/harness I would need to remove the grill, the upper intake, the power steering pump, heat shields, etc. I did poke and pull on harness in the area of each sensor and was not able to re-create the fault. While under the car checking the oil pressure switch harness it did seem a good time to look at the fuel tank harness before letting the car back down on the lift. The right front corner of the metal fuel tank shielding had sign of being hit in some manner and the harness just above that had a cut in the 5 volt reference circuit wire. The cut was laying on the sharp edge of the shield and occasionally shorting to ground. I had found the problem and repaired the wire, secured the harness in a better position, and cleared codes. 

 

Thanks for reading

Kenny@ggauto.repair

2006 Toyota Avalon V6-3.5L Misfire Complaint

 The customer complaint is a misfire. The check engine light is on and I'll check the stored engine codes. I can feel the misfire as I drive the car into the shop. Feels like one cylinder has dropped out. 

I got more that I was expecting. I was hoping for a code that would lead me to the misfiring cylinder without my having to check for myself. Instead I got misfire codes for every cylinder. 

I only currently have a misfire on one cylinder and I want to find that one since the problem exists now, while I am testing. I can't determine why there are misfires in the other cylinders while they are not misfiring. Work with what you are given. Now the scan tool can monitor current cylinder misfires so I looked there with the engine running and misfiring. I get something else that I wasn't expecting. I show no cylinders misfiring though it is indeed misfiring. 

 I'm left with determining which cylinder is misfiring by other means. Now, back in the old days I would disable a cylinder while the engine was running and listen for the rpm drop. No drop and there was the misfiring cylinder. When we had carbs and plug wires this was easiest to do by removing the plug wires one by one, either at the plug or at the distributor. Pull one, re-attach, pull next one and so on until you knew which cylinders were misfiring, or even weak contribution. As systems changed it turned to maybe disconnecting a coil, or an injector depending on what was easiest to access. The principal was the same. Kill that cylinder and pay attention to the rpms. (Remind me to tell you of grasping a plug wire on a Dodge Intrepid on a rainy day while standing in a puddle of water. I can tell you it is a very quick way to spot a bad plug wire.)

The process here is less intrusive and is done by commanding each injector to stop, one at a time, and note the rpm drop. (They call it commanding but it is more accurately, requesting.)  I found rpm drops on each cylinder tested except for #4. I found my misfire on #4 cylinder. Attached is the rpm drop with injector paused on #1. The rest would look similar so saving you the repetitive shots. I did want to include the misfiring #4 however a new wrinkle appeared. When I next started the car to get a screen capture during the test, it was no longer misfiring. It now became an intermittent misfire on #4 cylinder. At least I was able to find which cylinder was misfiring and I do know from the fact it is now not misfiring I don't have a compression or vacuum leak problem. I am looking at potentially an injector or ignition problem. I am leaning toward ignition since it does have the #4 ignition coil fault code stored as well. 

 The plan is to swap both the spark plug and coil from #4 with spark plug and coil from '#2 and see if the misfire moves to #2. This would be simpler if the misfire would return, versus my switching things while there is no misfire and waiting for it to come back. I gave the car several chances to miss and finally it did start to miss again prior to changing #2 & #4 coils and plugs. Here the miss if on #4. 

I removed both spark plugs and coils #2 & #4. The spark plugs are severely worn btw and I suspect are original with 211,066 miles. 

I swapped the #2 plugs & coils. If the misfire moves to #2 then the fault is definitely a bad coil and plug. 

Luckily I still have a misfire on re-start and it isn't on #4.

The misfire is now on #2. 

What will be needed here is new spark plugs and ignition coils. With the high mileage and worn plugs the coils have been stressed which caused the failure of #4. The rear plugs are very difficult to reach being under the intake manifold so the coils should be replaced at the same time to prevent having to go back and replace another failed coil very soon. 

Thanks for reading.

Kenny@ggauto.repair

845RE Park-by-wire malfunction Transmission Digest August 2024

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Codes vs Faults 2010 Dodge Ram

 This 2010 truck came in with three fault codes active. Instead of walking you through the testing, let's just go right to what was causing each code to set. 

Here they are: P0522, P1281 and P0456

P0522 was a leaking oil pressure sensor. 

P2181 was a poor connection at the coolant temperature sensor. 

P0456 was a bad gas cap seal. 

Now there was also a complaint of long cranking time at start, intermittently. These do have known problems with the fuel pump relay, which is built into the TIPM but the complaint could have also been caused by the poor coolant sensor connection. Since the problem hasn't appeared and since it could possibly be fixed via cleaning the connection, I've elected to do the wait and see option on that particular problem. 

Kenny@G&GAuto.Repair