Check Engine light

No its not stuck on, its stuck off. It does not illuminate briefly when you start the truck and thus will not pass a smog check in CA.

I'll be fixing this 1988 Ford Ranger P/U this weekend and having done some homework already, I still need a tip. As background this truck did have a problem where it just stalled out and wouldn't start again. That problem was traced to a wire harness that came loose and got burned on the manefold causing (at least) one of the wires to go open. Evidently the one needed to keep things running. That was fixed through visual inspection with a little help from a Ford explorer 1993 shop manual.

Now I suspect the check engine light problem is the same cause (open wire in harness) only I don't know which wire to trace. I checked several repair guides and none show the check engine light and what wire it is associated with it. If I could just determine the color and connectors it runs through this would be easy.

I'm not usually one to suspect conspiricy but really. WRT the ECC and associated sensors and idiot lights; Chiltons and Haynes only show a picture of some parts and say its too complicated to troubleshoot. OK expected. The FORD shop manuals for my 93 Explorer have a single page saying check the third manual (you don't have). The EVTM (electrical/vacuum troubleshooting manual) for the 84 Ranger (by ford again) shows most of the wires to the ECC but not the idiot light (check engine).

If anyone has the ECC repair manual for just about any ford truck (ranger, bronco II, Explorer in the 1983 to 1993 range you can probably determine the wire color for me.

Yes, I will check the bulb first. So far I have only visually traced the wire harness back to the ECC so it seems likely there is another open wire in there.

My second option is to trace the wire from the lamp back to the open using a signal tracer (triplett fox and hound). That will work but at the cost of more effort.

Does anyone have any insight as to why this indicator lamp would be excluded from most service manuals.

Reply to
pipedown
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Nope other than Haynes and Chiltons are not the first place I'd go for schematics.

Check out

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It's the online version of Mitchell On Demand and has the *actual* schematics. You can buy one week, one month or one year subscriptions. One week is $10, I believe. I just got a one month subscription for one of my vehicles for $15.00. and you can print whatever you need to, although I'm not sure how you'd go about downloading anything.

Reply to
scrape

Does it come on if you force a code, like say unplug the engine coolant sensor once tghe engine is at operating temp.

Whitelightning

Reply to
Whitelightning

Have you considered the possibility that the bulb is burnt out?

My vehicles turn the bulb on with the Ignition ON. The light goes out on my Jeep and my Mazda (a '94 and a '93, respectively) turn the light on with Ignition ON, then the light goes out after a few seconds. My '94 BMW turns the light on and keeps it on until Ignition START.

If your Check Light never comes on, the first check is the bulb. You had trouble previously though, so you may want to look at the melted wires again to be sure they were all fixed.

Reply to
Jeff Strickland

On Tue, 13 May 2008 13:00:20 -0700, pipedown rearranged some electrons to say:

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Select "repair info" You can get a basic wiring diagram there.

According to that, 1988 Ford Ranger, 4 cyl, check engine light is a pink wire going to pin 20 of the engine control module. The high side of the bulb is protected by a 10 amp fuse (fuse #10), check that fuse to make sure it is OK.

Reply to
david

No Chiltons and Haynes were my last try and just about all they had at the library ( I sent the friend whose truck I am fixing). I may try a subscription service if things get hairy next week but the friend is poor and we don't want to spend much if anything. Registration is payed. just need to pass smog to get a sticker, they give you a bit of time to clear that up.

Reply to
pipedown

I may try that but I suspect it will not. Seems like an easy test though.

Its either the bulb (maybe a fuse), wire or controller and I will check them in that order.

Reply to
pipedown

Duh, re read, I plan to check that first

Reply to
pipedown

That's a pretty good website but a little slow for me. I am still looking for the source diagram (do you have an exact link?) you quoted the pink wire but that info should be useful in and of itself. Thanks

Reply to
pipedown

I would not expect the Check light to be on its own fuse. It should get ground to turn on from the computer -- the pink wire -- If this is true, the pink wire should show 12v if the light works.

Reply to
Jeff Strickland

That's exactly what I expect. I think the ECC gets power directly from the ECC relay which goes through a fusible link (from memory the EVTM book is at home right now) which if open would do a lot more than extinguish the lamp. But an other poster did indicate fuse position 10 so its easy enough to check, that's an open item since I have not found the diagram yet.

My plan, remove dash, test bulb with DMM, test ground side connection with DMM, check for 12V on wire despite bulb. Connect FOX near bulb, trace wire with Hound to open (ideally) or back to ECC, verify ECC output with voltmeter. I see some ECC on eBay less than $50 incl shipping that should work for this vehicle and then there's pick and pull.

Indecently I did a diagnosis like this about 10 years ago on a GMC blazer. In that case the ECC had a burned out pin on the control IC chip (verified through electrical bench testing) so it had to be replaced. Instead the bum of an owner for that car rigged a switch and manually faked the operation during the smog test. (A bum for more than just that lame act)

Reply to
pipedown

If the circuit works as I suspect, the bulb will get its power from a buss that powers other lamps in the same area, but will get its ground from the computer. If this is accurate, you should be able to feel 12v sitting on the pink wire all of the time, and the light should come on if you pull the pink wire to ground. You don't have to take the dash apart to test the bulb. You do have to take it apart to replace the bulb, but if there is 12v sitting on the pink wire, the bulb is good.

____________ 12v | | lamp | | / |

------------ GND

In this really bad diagram, the computer is the position of the / and this represents the switching device that goes low to turn the lamp on.

There should be 12v above this point all of the time. When the / turns into | (the switching device closes) then there will be 12v on one side of the lamp and GND on the other, and the lamp will come on. The switching device is not really a switch at all, but it does the same job, it provides ground to a lamp that has 12v sitting on it keeping it ready to be turned on. If there is not 12v sitting on the pink wire, the bulb is bad or the wire is broken between the lamp and the connector. I'd consider the lamp first, but you said that the wire bundel has already had a repair because it fell across the manifold or something like that.

Reply to
Jeff Strickland

I understand but that 12V source will have at least one protection device and maybe a relay between it and the battery. The switch in your diagram would be the ECC pin.

Here are the wiring diagrams.

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I have looked at every one and I can find no check engine light. Pin 20 is always black and grounded, fuse 10 is for general exterior lamps (if used, diagrams disagree) and I can find no pink wire on any diagram. I am not so confident in finding a pink wire anymore. These diagrams are very similar to the ones in the EVTM

In any of the cases, it should be obvious as soon as I start probing the lamp. I have a clear plan of action when I start. I'll try to post results. Haven't looked at the truck in a few days.

Reply to
pipedown

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Oops, there it is on the first diagram, Duh

but only on that one, not sure which diagrams apply to this engine. I'll figure it out later.

Reply to
pipedown

On Wed, 14 May 2008 21:06:11 -0700, pipedown rearranged some electrons to say:

It's in the very first one that comes up.

Reply to
david

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I found the Check Light on the diagram without any problem at all.

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You are interested in Fuse 10, and Connector Pin 20 on the ECM.

This is on the left side of the diagram, near the top.

I don't recall the motor you have, so I selected the larger of the two 4 cyl options.

Reply to
Jeff Strickland

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I looked this morning. Fuse 10 spot is unoccupied and the sticker next to the fuse panel says #10 is for the rear brake towing option. I suspect that diagram only applies to the 83 model. I have the EVTM published by ford and nothing like the first diagram is included, the remaining diagrams match the EVTM very well. With no captions on the diagrams its partly guesswork. The engine is EFI and the controller is marked ECC IV.

Can't hurt to try a fuse in #10 but I have little hope it will lead to a 1 minute fix.

Reply to
pipedown

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My mistake, I thought you had an 83 Ranger.

Reply to
Jeff Strickland

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My mistake again, the diagram covers up to the 1990 Ranger/Bronco II.

Reply to
Jeff Strickland

So now I am perplexed. I pulled the dash and checked the bulb, it was good and powered from the high side same as a few other lights that do work like the check oil lamp. Then I identified the wire (pink/lt green) and traced it back into the engine compartment to the first connector. I get good continuity to that connector. The wire color and lamp match the EVTM for the 1993 Explorer up to that point

Now the crazy part, the mate to that connector has no wire in that pin location, no pin contact and the outside is plugged up so it was never there, not just broken. Furthermore, there is no PK/LG wire at the ECC or the self test connector as it would be if it continued to agree with the 93 diagram.

Pin 17 of the ECC which should have that wire has a tan/red wire that leads to the self test connector same pin but I don't know if simply connecting those nodes will result in the check engine lamp working or just burning out the pin.

I'll advise the owner to go back to the smog check place and try to prove there is no lamp. I bet that flees like a lead balloon. Maybe she can call and verify first. Given that I can't find any verified diagram showing the lamp, it might not actually be implemented. Can anyone conform or deny that? Anyone own a 1988 ford truck?

Reply to
pipedown

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