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Error Code P1506

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Gary Lewis

Error Code P1506

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Guys - As we were pulling into the lodge at Robbers Cave for the night after 225 miles of driving I was anticipating posting “Wonderful day and no problems found.” And the the Ewissions light came on.

I put the scanner on and got the screen shown below, and a search for that code says: “ P1506 indicates that the RPM for the engine is too high, while P1507 indicates that the RPM is too low. Both high and low RPM idle can indicate other problems within the engine, which is why these codes are frequently accompanied by other codes that indicate the actual issue within the engine.”

The DTC reset just fine, and I think what happened was that I was following a very slow lady into the lodge and let off the gas completely for several seconds while the momentum caused the engine to spin faster than the prescribed 648 RPM. Does that make sense?

Gary, AKA "Gary fellow": Profile

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI

salans7

Re: Error Code P1506

Where is the IAC from? Is it Motorcraft or aftermarket?

85lebaront2

Re: Error Code P1506

Administrator

In reply to this post by Gary Lewis

What it may be is the EEC is not aware that you are in gear and coasting. I don't know if there is a way to prevent that or disable it. The EEC is receiving "closed throttle" but the RPM is too high, so it shuts the IAC, RPM is still too high, so it says "problem".

Bill AKA "LOBO" Profile

"Getting old is inevitable, growing up is optional" Darth Vader 1986 F350 460 converted to MAF/SEFI, E4OD 12X3 1/2 rear brakes, traction loc 3:55 gear, 160 amp 3G alternator Wife's 2011 Flex Limited Daily Driver 2009 Flex Limited with factory tow package Project car 1986 Chrysler LeBaron convertible 2.2L Turbo II, modified A413

salans7

Re: Error Code P1506

Given all the recent messing around with the air intake tubing, I might also suggest looking around for vacuum leaks. This didn't seem to be a problem on all of the previous outings with the truck.

Gary Lewis

Re: Error Code P1506

Administrator

Shaun - It is a Motorcraft. But you are right, I’ll check to see if there’s something amiss.

Bill - We are thinking alike. If nothing shows up as being loose/off we will see if it reoccurs.

Gary, AKA "Gary fellow": Profile

Gary Lewis

Re: Error Code P1506

Administrator

I checked the air inlet this morning and found no problems. And thinking about it, nothing I did changed anything on the downstream side of the IAC. So I'm pretty sure it was nothing that I did.

Anyway, it started up just fine and ran all day with no error codes. I think it was a fluke.

Gary, AKA "Gary fellow": Profile

salans7

Re: Error Code P1506

It's always possible. I once had an ABS code that never came back.

Hopefully it stays away!

85lebaront2

Re: Error Code P1506

Administrator

In reply to this post by salans7

Shaun, on a Mass Air system, any leaks between the MAF and engine will result in a possible high idle and/or a lean condition as the MAF is what sets the base fueling, the O2 sensors fine tune it.

Bill AKA "LOBO" Profile

Gary Lewis

Re: Error Code P1506

Administrator

We are back home and are happy to say that the error hasn't occurred again. But, I have a different theory.

I was texting with my nephew, the mechanical engineer turned auto mechanic, and in the course of the to and fro he asked if the ECU can see the clutch. The answer is yes.

So, what if the ECU uses that input to determine if the engine is idling w/o connection to the transmission? And what if the clutch is still slightly engaged when the switch is triggered? In that case the engine could be overdriven by momentum of the vehicle while the ECU thinks it was controlling the idle speed. And in that case it would throw an error code.

Thoughts?

Gary, AKA "Gary fellow": Profile

salans7

Re: Error Code P1506

What allows the ECU to see the clutch? The clutch pedal position switch like on my Ranger?

Gary Lewis

Re: Error Code P1506

Administrator

Very good question, Shaun. And one I had to go back and research. From Jim's explanation here on how things work I then marked up the schematics shown below - with the Clutch Pedal Position Switch (CPPS) shown in the "up" or "clutch engaged" position. To summarize:

Disengaged: The clutch pedal has to be depressed to put the CPPS in the disengaged position so power can flow from the Start terminal on the ignition switch through the wire I show as green in the drawing to the start relay.

Engaged: With the clutch pedal up the ECU is "seeing" the unenergized coil of the Start relay via the wire I show as red, so the voltage to the ECU will be 0.

So the ECU knows whether the clutch pedal is depressed, at least to some extent, but it doesn't truly know if the clutch itself is disengaged. So if I depress the pedal enough to open the switch the ECU will think the clutch is disengaged. But if it isn't and if the vehicle's momentum causes the engine to spin faster than the idle set point then an error will be flagged.

Gary, AKA "Gary fellow": Profile

85lebaront2

Re: Error Code P1506

Administrator

Gary, another thought, two parts though, first, is there a way to have a "neutral" switch on the ZF, one that is either NC or NO in neutral, but the status reversed in any gear? Second, in the newer programming software, is there an "in gear" function for a manual transmission?

End result. if the transmission is telling the EEC it is "in gear", clutch switch is telling it, "clutch is engaged", can the software ignore the rpm discrepancy under these conditions and accept that you are creeping?

Bill AKA "LOBO" Profile

Gary Lewis

Re: Error Code P1506

Administrator

Bill - That's good thinking, but the ZF appears to just have the reverse switch. But I don't know about an "in gear" function on the ECU. I don't remember seeing one.

I think I'm going to wait to see if this happens again, and if so how often. If it is a problem then I might see about adding a switch that I can adjust and loop the circuit through it. With it adjusted so that the clutch pedal has to be essentially on the floor I shouldn't have any more problems.

Gary, AKA "Gary fellow": Profile

salans7

Re: Error Code P1506

In reply to this post by Gary Lewis

My Ranger is wired up the same way according to my diagrams, which doesn't surprise me considering my Ranger is using 1990s technology since Ford was terrible about updating the Ranger mechanically.

I'm generally curious as to how coasting would lead to an rpm overspeed error. If the shift lever is in neutral with the wheels spinning at decreasing speed, wouldn't the engine rpms drop to base idle since the connection (to the rear axle) through the transmission is "broken"? If the shift lever is dropped to a lower gear, the rpms rise, and then shouldn't they gradually fall as the momentum decreases? I can't see where the momentum of the vehicle would affect the rpm outside of the above two scenarios unless something was corrupted in the computer/electronics?

Just some food for thought, but I once had an issue where my rpms would "hang" when shifting to the next gear. There were no codes, so I couldn't quite figure it out until one day the truck just randomly struggled to idle and accelerate (still no codes) and I tracked it down to a dead spot just off idle in the throttle position sensor. I replaced it with a Motorcraft unit to fix that issue, and then realized a few weeks later that the new TPS had fixed my rev hang issue too. If it happens again, I suggest looking into the TPS. If it could affect my rpms between shifts, I'm sure it could affect your rpms while coasting. I never received an overspeed error, but my truck has a history of not throwing codes even when the engine is running terrible.

Gary Lewis

Re: Error Code P1506

Administrator

We were in 2nd gear coming down a slight incline and about to stop at the lodge to check in. I believe I had my foot on the clutch and probably had pushed it part way down. My guess is that I'd pushed it far enough down to trip the switch but not far enough to completely disengage the clutch, so the engine was still being driven by the momentum.

That switch also feeds the speed control, and I've frequently tripped it to kick the speed control off. That has worked fine with the speed control going off and removing throttle to the engine before the clutch disengaged. So I know that at least that part of the switch trips before the clutch lets go or the engine RPM would head north. And apparently the part of the switch that serves the ECU is about the same, meaning the switch trips before the clutch fully releases.

There may be an adjustment on the clutch, but it already has to be really close to the floor to start so I don't want to change it much. However if we have another instance of throwing a code then I'll probably see if I can adjust it a bit.

Gary, AKA "Gary fellow": Profile

salans7

Re: Error Code P1506

Gary Lewis wrote

We were in 2nd gear coming down a slight incline and about to stop at the lodge to check in. I believe I had my foot on the clutch and probably had pushed it part way down. My guess is that I'd pushed it far enough down to trip the switch but not far enough to completely disengage the clutch, so the engine was still being driven by the momentum.

Oh okay, that makes sense. Your initial description was missing the driver input which is what confused me.

I was misspoken earlier; my truck drops to around 1100 when coasting in neutral. Only at a stop does it come down to base idle rpm.

Hopefully you don't run into this issue again, but if so I'll be interested to see what was causing it.

Gary Lewis

Re: Error Code P1506

Administrator

Your Ranger is running the same code that I have in Big Blue. There's a setting, called Dashpot by the Core Tuning team, that keeps the idle up while coasting until you get to a specific MPH. You can adjust both the idle RPM and the MPH.

I had fits with that when I initially got BB running on the EEC-V system, and you can read about it in these "hits" on my search for "dashpot" in BB's Transformation thread.

And yes, I didn't mention the driver input as I hadn't thought that it might be important. But when I thought about the switch and the clutch I realized that there was more going on than I explained. And with all of that info it seems to make a complete picture.

Gary, AKA "Gary fellow": Profile

Gary Lewis

Re: Error Code P1506

Administrator

Had two more instances of the P1506 error code today, both while putt-putting around in 4Lo moving the trailer to get Steve's 1997 E-Series van. I'm pretty sure it is an issue with the clutch switch tripping before the clutch actually disengages, which causes the engine to be over-driven while the computer thinks it is running free. That causes the engine to spin faster than the idle set point and the computer throws the code.

So I need to spend some time adjusting the clutch switch - assuming that it is adjustable. We shall see.

Gary, AKA "Gary fellow": Profile

Gary Lewis

Re: Error Code P1506

Administrator

Another instance of P1506 today. I'd been idling in 1st gear and eased off the throttle. Apparently the momentum caused the RPM to go above the target.

I need to research this to see if there's something I can do in Binary Editor to prevent this.

Gary, AKA "Gary fellow": Profile