Carnac the Magnificent Mechanic

 Anybody remember when Johnny Carson would be Carnac the Magnificent? He would use his power of mind to answer a question before seeing the question. Always funny.

In a similar vein, I'm going to take a look at some information I have on a car that I have not seen. For instance a random car for sale online with a vin 2C4RDGCG7DR798845. 2013 Dodge Grand Caravan with 128,277 miles. 

Alldata tells me the van was serviced and battery replaced 7/10/25. Alldata also shows a technical service bulletin related to a flash update to the fold and stow module to address a problem with the module sometimes staying in wake mode and discharging the battery.

ShopKey Pro charts the mileage of battery replacements on these vans, easy to notice the peak times to expect a battery failure. 

Based on mileage we can also expect it needs brake pads and spark plugs unless they have recently been replaced. It is also worth noting that 128,000 is the peak mileage that a timing chain is often needed. Good things to bear in mind when you are shopping and considering this purchase. 

Cold Case #1 {2013 Chevrolet Equinox)

Not every car I do a diagnostic scan on gets authorized for further work but I still have the scan with no follow up. What if I explain what would be the next steps if the steps were made? Contrary to what you may see or hear, a diagnostic scan is not a diagnosis. It is a first step in making the journey to a diagnosis, and repair. Bear in mind, the car is no longer here but I have the scan. 

2013 Chevrolet Equinox 2.4 {186,372 mi}

I have 7 stored engine codes. 

 P0030, P0031, P0053, P0135, P0138, P0300, P0455 are the stored engine codes. 

P0030, P0031, P0053 and P0135 are all indicating a problem with the front O2 sensor heater circuits. That can be tested further by using a scan tool to command the heater circuit on or off and testing for power, ground and resistance at the sensor. Further testing would be based on the results. But we are forming the overall strategy at this time so let's consider the P0138. There we would want to monitor the rear O2 sensor voltage while engine is running and see just what the high voltage actually reads. If it is simply the sensor is indicating a high voltage due to a rich condition it could be related to the front O2 problem causing a loss of fuel control. A look at freeze frame data for the P0138 might also be helpful as this was a snapshot of the conditions present when the code set,. P0300 is a misfire code. What we should do from that is take a look at misfire history in the scan data and see if this is any particular cylinder(s) or spread throughout. If it is several cylinders involved it could also be related to the O2 problem. We also want to inspect the spark plug condition while looking for the misfire problem. Our job during the diagnostic phase is to find the items that are needed so be able to advise the customer of the best course of action. The P0455 would lead me to do an inspection of the EVAP hoses and connections, gas cap, evap vent and purge solenoids looking for any obvious problem. 

At this point we know:

 we need to inspect spark plugs and look for more misfire information

we need to test the front O2 heater circuits

we need to look at an obvious EVAP system problem (an EVAP problem has potential to cause a fuel control problem)

Once we have found and repaired the front O2 problem and misfire problem we can retest the rear O2 voltage to see if it is now good, or address that problem further if it still exists. Also, if the car did require a new front O2 sensor you must do a heater relearn reset so the car can adapt to the new sensor.

That may leave the P0455 for further diagnosis if the problem wasn't found on inspection.

Thanks for reading

Kenny@GGAuto.Repair

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

845RE Park-by-wire malfunction Transmission Digest 2024

Oil Life Monitors Shop Owner March 2025

Oil Life Monitors Shop Owner March 2025

Tesla service, repair, and diagnostics PTEN October 2024

Tesla service, repair, and diagnostics PTEN October 2024