No start - 121 anti theft code?

[Ilikemice]

I'm having yet another problem with the Ex...


It won't start. It happened to me Friday evening when I was trying to get home from work. The starter would work but I'd get nothing. I was getting spark, but I couldn't tell if the fuel pump was coming on or not.

An hour later the AA guy turned up and the car started fine so I drove home. The anti theft light stayed on the entire journey.

I try to start it yesterday and it cranks but doesn't start. I give up.

I try again today and it still won't start. I decide to recharge the battery after much fruitless cranking. An hour later I decide to try again and it fires up fine. It starts no problem over and over. This is where I'm at now.


The theft light is giving me a 121 code. It flashes three times then the light stays on. It does this when the ignition is on and when it's running, and the times when it decides not to start. What's the 121 code? The only reference to it I've found is an old unreplied-to post from a few years ago. The 121 engine code is something to do with a bad TPS apparently.

I guess the light is something to do with the no-start... I'm also guessing it could be fuel related. Is there any way to test if the fuel pump is working? I can't hear a pump noise even when it does decide to start.

Cheers!

 

[chrisquelch]

hi i would start by checking the crank position sensor for good connection and no mud over it (dirtiest engine compartment winner )then the cam position sensor for connection if the pcm doesn't get input from cps i don't think the pump runs.cheers chris

 

[kevin p]

I agree with Chris. Mine used to be a dodgy starter. It would or it wouldn't. I took the crank sensor connector off and on a few times and sprayed some switch cleaner on the contacts. Its been perfect since.
Kev.

 

[Stenasev]

Hi,

Code 121 is a fault between the main immobiliser and the coded fuel pump relay. This would explain why it is not starting even when the starter is turning and you are getting a spark. Obviously the fault is intermittant as it is starting sometimes. If the crank sensor was at fault then it wouldn't be sparking.

SS

 

[Ilikemice]

Thanks all. The immobiliser problem seems to be the culprit, as the two sensor contacts appear fine.

Where would I begin looking for the issue? Am I looking for continuity between two wires somewhere?

 

[jcasey007]

I had the same code after I jump started the car after leaving the lights on all day, I pulled the battery + lead off for 10 mins, replaced it and no more code.

BTW the easiest way to see if there is power going to the fuel pump is to either put a meter (volt setting) or a 12V bulb with some wires attatched between one of the connections to the inertia cuttout switch and earth.

when you turn the ignition key to the position before cracking, the bulb (or meter) should show power for about 4 seconds (priming the fuel pump before starting) and when you crank the engine it should also be on while you are cranking.

I fitted a switch in line with the inertia switch (to manually cut off power to the fuel pump)which has an LED in the end of the switch arm, so I always know when power is going to the pump

cheers

J

 

[Ilikemice]

Update:

There's power going through the fuel pump cutoff switch and across the fuel pump fuse. I dropped the fuel tank and took the pump and assembly off. The pump motor works when jumped across the terminals at the top, but there's no continuity and it won't work when reconnected and jumped using the harness connector unplugged from the frame.

I'm guessing the box on top of the fuel pump assembly is some kind of relay which is breaking the circuit. Is this right? The wiring diagram I've got just says "1996 Explorer" and according to that the box on top doesn't exist.

Where do I go from here? I haven't been able to find a wiring diagram which includes the immobiliser stuff yet.

Cheers!

 

[Stenasev]

Update:
I'm guessing the box on top of the fuel pump assembly is some kind of relay which is breaking the circuit. Is this right? The wiring diagram I've got just says "1996 Explorer" and according to that the box on top doesn't exist.
Cheers!

This is what I mentioned in my earlier post. It is known as a "PSM". If you just want to bypass it to cure any fault then cut and join two of the wires coing out of it. You need the pink/black and the white/red. These will be the biggest of the wire guages used.

SS

 

[Ilikemice]

Awesome thanks!