I'm wondering if someone in this forum would be able to advise me how to continue troubleshooting.
My Expedition 2009 does not start. I assume that's because the starter relay is not properly grounded. The reasons why I think so are) 1. The relay put somewhere else works and healthy relays put in the starter relay slot don't work) 2. The "ground" pin in the relay socket is 1.5V above the ground so that when ignition is turned on the steering voltage is 1.5 lower) 3. When I connect the relay ground pin to the battery ground starting working.
Any idea how this could have happened and how I could get this fixed? The wiring below the fuse box in motor compartment seems to be quite dense so that I don't feel confident disassembling it for further troubleshooting.
Thank you, jiri
The starting system ground is controlled by the PCM. The ground on the relay goes directly to the PCM.
The ground circuit schematic I am sending you has three related items that are part of the starting ground circuit, the PCM, the data link connector (check the ground terminal) and the transmission neutral safety switch. If the natural safety switch is malfunctioning the PCM will think the truck is not in park or natural and will not enable the ground for the starter relay. I am only mentioning this because it is in the circuit so check it to be safe.
Check the grounds from the battery to the body and frame. Then check the body ground going to the PCM and then check the ground from the PCM (Yellow wire) to the ground terminal on the starter relay terminal number 2.
If you checked the truck with a scanner you might find out you may not be able to connect to the PCM because of the poor ground at the data link connector. If you can connect see if there are any trouble codes set in the PCM memory.
From what you are telling me is the voltage drop is 1.5 volts which would indicate a poor ground.
Check out these suggestions and get back to me with your results.
This is the power circuit schematic.
Schematics supplied by the Alldata automotive information website.
Morning, it seems that PCM, frame and body are relayed, yet there is +1.5V voltage against the battery ground coming from the pin#7 over the yellow wire to the starter relay pin #2. Any idea?
Thanks a million, jiri
If you don't have a good ground at pin #2 at the starter relay the ground comes from pin #7 at the PCM. If the ground coming from pin #7 is not good then either the ground to the PCM is bad or the PCM is bad itself.
Can you put a scanner on the truck to see if you have any trouble codes?
Taking your car to a mechanic for a second diagnostic opinion may be worth the diagnostic fee they will charge. It could save you money in the long run.
Yes, the +1.5V ground (Against battery) comes from the pin #7 at the PCM connector. Also the PCM seems properly grounded . I measured against the plate on which the connector brackets are mounted. (see picture)
I should have mentioned too that the wrench symbol appears on the console and while I'm not entirely sure, the starting problem could have started appearing after a workshop was fixing a transmission gauge. (there is a gauge leading into the transmission, the sealing at the entrance point was broken, therefore there was a minor oil leak and they fixed it somehow).
Any idea how to narrow the problem further? Did you mean OBD/II diagnostics by "scanner"? The last time I checked I didn't see any unusual code.
Thanks a lot, jiri
If you are doing a voltage drop on the ground to the PCM the voltage you are showing me is too high. A voltage drop should be less then .5 volts, the reading you are showing me is 7.8 volts. If work was previously done to the truck you would need to check the work done. It is possible the body ground was left loose or is dirty or corroded.
Try running your own ground with a jumper wire to the PCM and see if the truck starts or if anything changes for the better like the voltage drop on ground wire #7. If it starts then find the bad ground.
If you can see if there are any diagnostic codes it would help a lot.
I know repairs on a vehicle can be expensive but it might be a good idea to have a mechanic check the truck out and get a second opinion on the no start problem. Paying the diagnostic fee to find out what the problem is can help you save time and then you could do the repair yourself to help save money.
The 7.8 is in _mV_ -- so it is as good as zero, I should have highlighted that. I will read the recent OBD/II codes if there is anything useful. It is not really about cost of diagnostics, I'm somehow worried that I observe this issue since the last time when I left the truck in the workshop :-Z
Further investigation on your problem led me to the area of the vehicle immobilizer.
When you put your key in the ignition do you see the green key or symbol on the dash board with the key in the ignition and the ignition on engine off. If you see the green key or symbol flashing then you may have a problem with the immobilizer system.
A simple test you can try is to try another key to see if the car starts.
I am giving you a description of the antitheft system supplied by the Alldata information website. I hope this helps.
Passive Anti-Theft System (PATS) Function
The PATS function is controlled by the IC. The PATS uses the IC to carry out all of the PATS functions, such as receiving the identification code from the PATS key, issuing a signal to the PCM to control the starter and fuel injectors enable, and initiating the key interrogation sequence when the ignition key is turned to the ON or START position. Because of the interaction between the IC and the PCM, there are parameters that must be set if the IC or the PCM (or both) are replaced. Refer to Passive Anti-Theft System (PATS) Parameter Reset. If the IC must be replaced for any reason (PATS concerns or IC concerns), the PATS keys also must be programmed into the new IC. Refer to Key Programming Using Diagnostic Equipment. All elements of PATS must be functional before the vehicle will start. If any of the components are not working correctly, the vehicle does not start.
PATS is active only for a few seconds when the vehicle is starting. It is not a PATS concern if the vehicle stalls after it has been running for a minimum of 3 seconds. PATS does not disable a running vehicle.
PATS may cause a vehicle no start due to either the fuel injectors or the starter not operating (starter relay does not close) or both. Always check for PATS DTCs from the IC and DTCs from the PCM when a no-crank or no-start condition exists. After a valid key read has been completed, low battery voltage may cause the PATS to allow starter operation, but prevent the fuel injectors from operating.
If the anti-theft indicator does not prove out (it may be either flashing or glowing steadily) and one (or both) of the previous conditions (fuel injectors and/or starter inoperative) are present, it may be due to a PATS issue. If the anti-theft indicator proves out, it may not be a PATS issue. If the anti-theft indicator does not illuminate at all, it may be a circuitry/IC issue.
PATS is not compatible with aftermarket remote start systems, which allow the vehicle to be started from the exterior of the vehicle. These systems may reduce the security of the vehicle, and also may be the cause of no-start concerns. Remote start systems must be removed from the vehicle before any PATS-related no-start concerns are investigated
Thank you for keeping thinking with me
"Unfortunately" the immobilizer seems OK. a replacement key behaves the same way and no light flashes.
So I will have OBD/II codes re-inspected -- in fact, I have done that using "OBD Auto Doctor" and haven't found any critical alarm; that could be perhaps an error in the diagnostics software too -- it crashed too often to be credible.
The 1.5V voltage on the PCM connector pin #7 seems to suggest that either PCM is broken, or some input to it. (PCM ground seems real.) So a question to myself is whether this is a PCM "bug" or PCM "feature". Could the PCM want to send "bogus" ground to the starter relay to prevent starting under some conditions it considers undesirable? I suspect if it was the case, it would send higher voltage with 1.5 the car occasionally starts, very sporadically but it does.
Reviewing the whole thread back to the beginning: so if the #7 PCM pin leading to the starter relay is non-zero, where can I measure the other pins that affect it? (data link and automatic transmission). Somehow the circumstance that the transmission gauge was replaced due to an oil leak makes me think of this part again.
Did I measure the PCM ground correctly by measuring the metal plate on which the PCM plug (and two others) is mounted?