Hello everyone,

I have the 98 Ranger with the 4.0 and ive gotten the dreaded 340 code ever since and after replacing the sensor/synchro twice. I have the three wire sensor correct me if im wrong but shouldnt there be a groun,signal and power wire? Im getting ground on two of the wires. Is this normal, and also what are the wires and voltages they should have. which wires do i need to check from the pcm to the sensor?


thanks a million JS

 

Welcome to FTE.

I see you don't have any replies yet, so I'll see if I can get things started.

Go here Search Wiring Diagrams & enter your vehicle info & have a look in Engine/Fuel Controls for the cam sensor circuit wiring & wire color codes.

 

Where are you here https://www.obd-codes.com/p0340, on the list of suspects?

 

Awesome. Thanks for the reply.

When I tested the connector I learned I have ground also on 282 db/o the cmp sensor shield wire. Is this normal? (doesn't seem like it should be) What voltage should the signal wire have on it with the key on not running? I'm assuming the s109 is the signal wire do you know how to tell what other sensors are on this wire as well, I know they use one wire,
o send signal to sensors sometimes. I've already replaced the crank sensor as well just to rule that out. I know it doesn't rule out a possible short on the crank sensor wiring if the cmp shares the same signal wire as ckp. Again thanks a million for the reply. [img]webkit-fake-url://766753d9-c92f-4c47-914a-3c6af3385fd5/imagepng[/img]

 

The DB/O wire should Not be grounded. If it is, then it's output to the computer is shorted to ground & is missing & the computer won't like that. Seeing as the P0340 code is for the cmp Circuit, it means the Wiring & connectors also belong High up on the suspect list.

Lets think about this some more, did this problem come about suddenly after some event, or slowly over time?

Don't toss any more parts at the problem on a hunch, right now it sounds like you may have a wiring problem with the DB/O cam sensor wire to the engine computer, being shorted to ground, so check it out for cut or damaged insulation, like a pinch or rub through spot from where it passes over, or close to a heated area, or is touching or rubbing something that moves or vibrates
.
With your multi-meter in the audio Buzz mode, disconnect the CMP sensor & give the DB/O wire, or wiring harness run a wiggle, or a not too strong pull test, & listen to determine if you can cause the short to clear, when you hear the meter buzz stops.
If no joy, disconnect the computer firewall electrical connector & see if the buzz stops. If it does, the problem is in the computer end of the circuit. If it continues to buzz, the problem is in the DB/O wiring run between the computer firewall electrical connector & the CMP electrical connector. So carefully inspect the DB/O wiring run for insulation damage.

More thoughts for consideration, keep us posted on your trouble shoot.

 

Ok so I was wrong. It's the LB/O wire that's grounded. Isn't that the 5volt signal wire?

 

I unhooked the pcm and the ground goes away. Does this mean my o man is bad? I'm assuming so.

 

The CMP does not share a common "Vref" circuit like some other sensors do. The CMP sensor is instead powered with ~12v from the LB/O wire. So you'll want to check for at least 10.5v on that wire. The BK/W wire is sensor ground.

Per the wiring diagram, it looks to me like the DB/O (CMP signal) wire shield is indeed grounded; the wire inside is not.

There are some videos online that purportedly show how to check integrity of the CMP signal. See, eg.,

 

I dont have a mult meter like his, mine is all digtal. But i ran the test and the voltage was extremely sparatic, i dont think i seen 12 volts one time while turning it over. So i think my pcm is bad, due to the fact that when I unhook it the ground im gettin on the LB/O wire goes away also i have every o2 sensor code there is. I t hought this was due to the fact its running badly but upon opening up the wire loom i seen that the LB/O wire is shared by the upstream o2 sensors as well as the cmp and a couple others that i didnt trace down. What all info. do i need off my pcm to find one i can use? thanks!!

 

You didn't mention the O2 sensor codes before...are there any other codes?

Yes, the 02 sensors share a 12v circuit with the CMP and some other things.

Since you are getting various codes that are common to that 12v circuit, I'd hold off on condemning the PCM until you ascertain that it's not a problem (fuse, wiring) with that circuit.

You will find the 15A fuse for that 12v circuit in the engine compartment fuse box under the hood (location #13 inside the box). The '98 Ranger owners manual has diagrams showing the fuse/relay boxes and locations.

 

It might be helpful if you'd post All trouble code Numbers you've found, as they can often provide clues that can help focus a trouble shoot.

 

After re-reading my 1st reply to this post, I see it may not have been clear, as I didn't directly answer your question about if the DB/O wire Shield should be grounded.
The shield around a wire is to prevent it from acting as an antenna & picking up EMI = Electro Magnetic Interference, or RFI = Radio Frequency Interference, which could corrupt a sensitive but weak signal, that wire is carrying.

SO Yes, a Shield should be grounded, as the wiring pictorial shows & as Rockledge replied. As I replied & as shown in the wiring pictorial, the Center Conductor of the DB/O wire Should Not be grounded.

Seeing as you've posted that DB/O center conductor Isn't showing a ground with the firewall computer electrical connector removed, it says the CMP sensor & wiring are ok, but the problem seems to be on the computer side of the circuit.

Seeing as you've reported Other trouble codes with O2 sensors that also use the voltage feed that's on the DB/O center conductor & that you say the 12 volt feed is intermittent & as Rockledge has suggested, Don't condemn the computer yet.

As it's now sounding like the problem may be with the 12 volt feed that the DB/O center conductor is supplying the CMP sensor & seeing as how that 12 volt also feeds the heated O2 sensors you say you've had problems with, it sounds like you may have a 12 volt feed problem that's upstream of the computer, or with other items loading that feed, like the O2 sensors that are being fed off the same B+ source, that might be loading that circuit, or causing electrical noise on the DB/O wire that's corrupting the CMP signal to the computer.

SO, as suggested in my above reply, post up All trouble code Numbers, as they can help focus a trouble shoot.

 

So after checking the 15 amp fuse that rockledge said to check I found that the fuse had not blown but had been hot enough that it had melted some.

Here re are the codes it's throwing
p0340
p1409
p1451
po135
po141
po155
po171
po174
thanks for all the help!!

 

Ok good feedback on the fuse condition showing it's been running hot. Other members have reported corroded fuse connections in their under hood power distribution box, so remove the fuse in question & check it's contacts for loose fit, or corrosion on it's power distribution box contacts. They should be clean, bright & tight so the fuse blades are making a good clean & snug connection.
Good idea to post All of the trouble code Numbers, so lets see what they suggest.
We are to work & put right the lowest trouble code number/s first & work our way up the list.
P0135 = Cyl bank 1 O2 sensor 1 heater circuit malfunction.
P0141 = Cyl bank 1, O2 sensor 2 (after cat converter) heater circuit malfunction.
P0155 = Cyl bank 2, O2 sensor 1, heater control circuit malfunction.
P0171 = Cyl bank 1 System too lean.
P0174 = Cyl bank 2 System too lean.
P0340 = Camshaft sensor circuit malfunction.
P1409 = EGR vacuum control regulator control circuit fault.
P1451 = Evap canister vent solenoid circuit malfunction.

SO, as Rockledge has supposed & you found with the over heated look of the 12 volt system fuse, it looks like you have a 12 volt feed load problem to things that are acting out. Question is where in the circuit does the problem lie. We need more clues, so as previously asked, has the problem come about suddenly after some event, or slowly over time?
Anything happen like a wreck, off road event, maintenance, or repair just prior to the problem showing up?

 

EUREKA!!!! Upon unhooking the fuse box that's under the hood and turning it over and unsnapping the bottom guess what wire isn't hooked up...? The LB/O wire that's hooked to the 15 amp fuse that's the same one that's been hot and is also the feed for the circuits in question!!!! Fixed that issue cleared the codes and drove it for 20 min and no codes or pending codes...fingers crossed this was the issue. Thanks for all the info and help guys!!!