Cold Codes: P0406

I've been working with trouble codes and self-diagnostic systems since.. well, since they became part of car repair. The earliest systems were very different than OBDII. With OBDII there are more standardized aspects to testing. For instance, generic OBDII trouble codes all mean the same thing no matter the manufacturer. A P0406 breaks down to, P=Powertrain, 0=Generic, 4=Auxilary Emissions. The last two digits, 06 define the problem; EGR Position Sensor Circuit High. Notice that it does not say the problem is a bad EGR valve, a bad PCM, or anything about what is needed to repair the problem. The PCM uses a voltage signal output from the EGR position sensor to verify EGR valve operation. The code description is saying that there is a problem with the sensor voltage on that circuit. I will step back just a bit more, it is saying that there MAY be a problem with the sensor voltage on that circuit. Finding why the code set instead of what the code is, that is where actual diagnostics begin. The code P0406 means the same for each manufacturer but the system in place for EGR sensor monitoring would likely be different, which would make the testing different. The next step would be to verify the problem. 

A 2011 Jeep Wrangler, 4x4 3.8:

On the Jeep you would need to monitor the sensor signal looking for not only the correct voltage while commanding EGR but looking with a scope for a clean signal. From that point, you go where your testing takes you. I will say that on the Jeep it is indeed usually a bad EGR position sensor, which is part and parcel with the valve itself. 

On other makes the wiring would vary but you would still be looking for the EGR position signal and for a problem with that signal. 

2005 Impala:

On the Impala the sensor is usually fine but the EGR valve is sticking. Still, both parts are made together. Do the testing and know what you need. Always remember that a trouble code is there to steer you to the system where a problem may be. It isn't there to tell you what you need to fix the problem. 

Thanks

Kenny@ggauto.repair

Let's Talk Codes: '06 GMC Sierra P0030

 The very best way to find the problem causing a Malfunction Indicator Light (MIL) to be on is to understand the system, how it works and what it needs to be looking at to set a particular code. First, find what codes are stored. You are going to need to listen to the story of any work that was done, any parts replaced, sensors disconnected, batteries disconnected, etc. because those sorts of things could obscure codes, set codes unrelated to the problem and generally cause diagnosis to be more difficult. The best scenario is that no one has been trying to repair the problem and you are looking at relevant data. There are times when the data looks a bit suspect and you may need to clear the system and let it begin from scratch. From there, run the monitors and look for a MIL to come on again. Experience is your best tool to make that judgement. 

So, in this case we want to determine the cause of the MIL Check Engine light. I used a full function aftermarket scan tool because it will be tossing a wide net and querying other modules for codes as well as the engine module. There are times that diagnosis can be made more easily when several modules store codes that could be related. In this case I think I can concentrate on the powertrain codes. 

Generally when you have several trouble codes you start with the lowest numbered code. In this case, P0030. I would expect that P0053 is a very similar set of conditions and that the two are related to the same problem. Now in the conglomerate of minds that come together via the internet you may have been told that a trouble code tells you what your car needs. That isn't true. While trial and error guessing could be considered a diagnostic approach, it is a very poor one. Better is to understand what you are looking at and how to test the system. Both the P0030 and the P0053 indicate a problem with the heater circuit of the bank 1 sensor 1 heated oxygen sensor. This would be the upstream fuel control oxygen sensor on the driver side exhaust. The power feed comes from the O2a fuse and powers both B1S1 and B2S1 sensors. Each sensor is grounded through the ecm at a different terminal. Since we have no B2S1 code the fuse is good. The only power related problem would be wiring or connector to the B1S1 downstream of the fuse. We can check power and heater ground with a meter and a scan tool commanding the heater on. The codes indicate the heater resistance is out of spec at startup and on engine running. Two seconds at startup sets a P0053, and six seconds of out of spec running sets a P0030. The O2 heater can be commanded on with the scan tool and monitored with a meter. If the power is reaching the sensor, and if the ecm is capable of grounding the heater circuit to the sensor then the heater resistance should be within specs. If it isn't then the sensor is bad. If it is then verify the ecm is measuring the current correctly. 

In this case the B1S1 heater was bad. Replaced sensor. 

P0449 indicates the evap vent canister solenoid control circuit did not match the command. Battery + feeds the solenoid and the ecm expects to see that voltage on the command side when the solenoid is commanded off and ground on that side when the solenoid is commanded on. A scan tool can be used to make the commands and the circuit monitored with a meter to find the problem. 

In this case the vent solenoid was bad. Replaced vent solenoid.

Kenny@ggauto.repair

Diagnostic Tech: 1999 Ford Escort (originally published Aug 13, 2007)

 Today's project is a 1999 Ford Escort ZX2 with 2.0 vin 3 engine and with automatic transmission. The complaint is that the A/C is not cold. The blower works. The air flow is good and from the proper vents.

One of the other techs here in the shop has made some initial checks and informs me that there is sufficient refrigerant in the system but the compressor clutch does not engage. With that information I run a simple test on the drive into the shop. I make sure the A/C is turned off before I start the car and on the way into shop turn the A/C on. I'm listening for the radiator fan to run. It does run. The radiator fan is turned on when I turn the A/C on. Why is that important? I'll get to that.
On this car (and on most cars) you aren't actually turning the air conditioning on when you turn the switch on. You are sending a signal to one of the control modules "requesting" the A/C on. Under normal conditions the control module "sees" the request, checks that conditions are met to allow air conditioning to operate and THEN operates the air conditioning system. If the control module sees a condition that isn't within specifications, such as a low refrigerant condition, it won't command the air conditioning on.
The powertrain control module is the module used to control the compressor and fan systems on this car. When the PCM sees a request voltage at its connector pin 41 and it sees no reason not to run the air conditioning it should do two things that are important to this diagnosis. It should command the compressor clutch on and it *SHOULD COMMAND THE COOLING FAN ON*. The fact that the fan came on with the A/C switch turned on means that the control switch works and that the PCM sees no reason not to turn the compressor on. It even verifies the pressure switches are fine because the request voltage from the switch must pass through the low pressure switch and high pressure switch on the way to pin 41 of the PCM.
Since I know the problem is on the PCM output to compressor clutch side of the system the best place to do some tests is at the constant control relay module. The relay module is a true black box containing several relays and mounted directly under the air cleaner housing at the left inner fender. The PCM may be the one making commands but the constant control relay module is doing the work.

Pin 21 of the CCRM is the power feed to the clutch relay inside the module. It should be powered with the key on. This is easily checked with a circuit tester and there is power to the relay. When the relay is closed the power feed to pin 21 should be fed to pin 23 and on to the compressor clutch. When I apply power to pin 23 the clutch does work so I know the wiring to the compressor is good. Since I have power to the relay and know that the clutch will work with power then I know that the relay is not closing. To close the relay needs a ground signal at pin 22. This signal should come from the PCM. It is the "command" for the compressor clutch to operate.

The coil side of the relay is provided power by the PCM power relay. This means that with the engine running and the A/C switch off there should be voltage at pin 22 of the CCRM. With the A/C on and the PCM commanding the relay closed there should be a ground at pin 22. With the Power Probe circuit tester I find I have everything I need at the relay to make the relay close. The relay has failed. Since the relay is integral to the CCRM the entire module should be replaced.

Kenny@ggauto.repair