CEL Code P1531

[Nick at da Mill]

We have owned a low (very - 22,000 miles in 9 years) mileage 1999 2.5 liter RHD (we live in Scotland) Boxster since new.

Two days ago, we drove at constant highway speeds (e.g., 80 mph) for oven an hour, before leaving the highway and coming to a stop at a red traffic light. At that point, the engine started idling very roughly (sounded like a timing problem), but with no detectable (tach. or ear) changes in rpm. After several seconds the Check Engine Light (CEL) started flashing and then came on solid. I pulled off the road, and checked the manual, which indicated I should take the car ASAP to a Porsche Service Center. We had little option but to continue on to our destination, during which the idling problem did not re-occur, nor was there any noticeable loss of power.

Since we were away from home, I looked for a local Porsche dealer in the telephone book. I ended up talking to a most unhelpful service adviser (that's what his badge later said), who said I could bring it in and they would check the failure codes. Needless to say, he gave no indication of how long I would have to wait. After an hour of drinking coffee and reading newspapers, he finally fessed up that it would be at least 2 hours more. So I called a friend, who picked me up, and said I would be back the next morning.

Upon picking up the car the next morning, I faced a bill for £174.49 ($321.06 this week) and the following information.

1. The PIWIS tester indicated that the car had recorded a P1531 diagnostic code.

2. They had "raised the vehicle to check the vari cam actuators as per diagnostic procedure code P1531"

3. The car required a new "actuator bank 1". Fitted cost = £617.90.

I tried to get some indication from the "service adviser" as whether they had detected a hard fault or an intermittent fault, to no avail.

In any case, that had reset the CEL and we drove home (more highway driving followed by red traffic lights) with no detectable rough idling or the CEL re-lighting.

My gut sense is that for some reason the vari cam actuator or a solenoid (are they different ?) got a bit sticky, and didn't revert to the correct position in one instance while idling, and that this condition has not re-occurred.

So I have two questions for the forum.

1. Can a visual inspection as per "2" above provide any real information on the state of the actuators?

2. Am I correct in thinking this was a single event, and can ignore it until, and if, it re-occurs?

[RFM]

The fault looks intermittent since the engine runs normal after the reset, you can check the wiring for damage and clean the connectors at the same time. I should wait for a intervention till the fault reoccurs.

[Nick at da Mill]

Not wishing to pay another £174.00 to read out codes and reset the CEL, I've invested in

1. An ELM 327-based USB to ODB II cable (£12.00 from China).

2. ScanTool Freeware (which allows me to read OBD II DTCs and clear the CEL).

3. The Porsche Boxster Technical Manual (£9.95 from workshopmanuals.biz)

A CEL event (flashing CEL) is now occurring occasionally when the car is restarted after a moderate (>20 minute) run. It does not occur when the car is cold, or as previously, when idling after a long run. ScanTool using the EML 327-based cable reports three DTCs (P0301, P0302 & P0303) which are mis-fires on cylinders 1-3.

So I have a number of questions.

1. Are the Bank 1 Camshaft adjustment manufacturer's codes (P1530 & P1531) available to a stock OBD tool?

E.g., does their absence in an OBD scan indicate that they have not occurred? Are they read by commands that I could add to the scan?.

2. Some of the Variocam literature describes it as "continuously-variable" valve timing. Is this really the case? For this to be

achieved, the ECU would have to vary the voltage/current to the solenoid, so as to achieve a desired valve angle as

reported to the ECU by the passage of Camshaft-attached tabs and windows through the air gap of the Hall effect sensor.

Is this really the case? If it is, then are the warm start and cold start valve angles commanded by the ECU different?

3. Do DTCs (P1530 & P1531) indicate that the ECU is not seeing the valve angle change (as reported by the Hall effect sensor)

as expected in response to solenoid input?

Thanks in advance for your answers.

Nick

Edited November 3, 2008 by Nick at da Mill

[Loren]

Not wishing to pay another £174.00 to read out codes and reset the CEL, I've invested in

1. An ELM 327-based USB to ODB II cable (£12.00 from China).

2. ScanTool Freeware (which allows me to read OBD II DTCs and clear the CEL).

3. The Porsche Boxster Technical Manual (£9.95 from workshopmanuals.biz)

A CEL event (flashing CEL) is now occurring occasionally when the car is restarted after a moderate (>20 minute) run. It does not occur when the car is cold, or as previously, when idling after a long run. ScanTool using the EML 327-based cable reports three DTCs (P0301, P0302 & P0303) which are mis-fires on cylinders 1-3.

So I have a number of questions.

1. Are the Bank 1 Camshaft adjustment manufacturer's codes (P1530 & P1531) available to a stock OBD tool?

E.g., does their absence in an OBD scan indicate that they have not occurred? Are they read by commands that I could add to the scan?.

2. Some of the Variocam literature describes it as "continuously-variable" valve timing. Is this really the case? For this to be

achieved, the ECU would have to vary the voltage/current to the solenoid, so as to achieve a desired valve angle as

reported to the ECU by the passage of Camshaft-attached tabs and windows through the air gap of the Hall effect sensor.

Is this really the case? If it is, then are the warm start and cold start valve angles commanded by the ECU different?

3. Do DTCs (P1530 & P1531) indicate that the ECU is not seeing the valve angle change (as reported by the Hall effect sensor)

as expected in response to solenoid input?

Thanks in advance for your answers.

Nick

1. Available - yes. Can all generic code readers read them - probably not.

2. Here is Porsche's brief description of Varicam

"VarioCam, the adjustment of the intake camshafts at engine speeds of approx. 1,300 rpm* and 5,920 rpm, produces a major part of the engine output, the engine torque as well as the good exhaust values at idling speed. Engine speeds below 1,300 rpm produce a slight overlap in the valve stroke curves for the intake valves in relation to the exhaust valves.

This particularly affects low proportions of hydrocarbons (HC proportions) in the exhaust gas before the catalytic converters. If the engine exceeds the 1,300 rpm mark *, the intake camshafts are adjusted by 12.5° (by 25° if measured a the crankshaft).

Adjustment of the camshafts to produce a greater overlapping of the valve stroke curves for the intake and exhaust valves results in improved cylinder charging and thus an increase in engine torque. In the case of engine speeds above 5,920 rpm, the intake camshafts are returned to the basic control times (as for engine idling speed). If the intake valve closes later, additional amounts of intake air can be drawn in. This produces a recharging effect since the flow of air is not interrupted. This also results in improved charging of the cylinders and an increase in performance.

* The value 1,300 rpm increases to 1,480 rpm with engine oil temperatures of approx. 133°C."

3. P1530 and P1531 means the actuator failed to move on command.

[Nick at da Mill]

Loren,

Thanks for your response.

1. Available - yes. Can all generic code readers read them - probably not.

Hmm. I managed to find a description of OBD Commands and Responses on pages 23-27 of http://www.elmelectronics.com/DSheets/ELM327DS.pdf.

Based on this description, there is no very good reason why any scanning software would fail to report OBD TDCs as long as: 1) Porsche is reporting them in response to OBD mode 03 commands, and 2) the software reads beyond the first three (each mode 03 command reads out three DTCs). Next time the CEL lights, I'll try reading them out using native OBD commands and responses, and see what turns up.

2. Here is Porsche's brief description of Varicam

"VarioCam, the adjustment of the intake camshafts at engine speeds of approx. 1,300 rpm* and 5,920 rpm, produces a major part of the engine output, the engine torque as well as the good exhaust values at idling speed. Engine speeds below 1,300 rpm produce a slight overlap in the valve stroke curves for the intake valves in relation to the exhaust valves.

This particularly affects low proportions of hydrocarbons (HC proportions) in the exhaust gas before the catalytic converters. If the engine exceeds the 1,300 rpm mark *, the intake camshafts are adjusted by 12.5° (by 25° if measured a the crankshaft).

Adjustment of the camshafts to produce a greater overlapping of the valve stroke curves for the intake and exhaust valves results in improved cylinder charging and thus an increase in engine torque. In the case of engine speeds above 5,920 rpm, the intake camshafts are returned to the basic control times (as for engine idling speed). If the intake valve closes later, additional amounts of intake air can be drawn in. This produces a recharging effect since the flow >of air is not interrupted. This also results in improved charging of the cylinders and an increase in performance.

* The value 1,300 rpm increases to 1,480 rpm with engine oil temperatures of approx. 133°C."

Thanks. From this description it would appear that: 1) there are only 2 variocam positions corresponding to "solenoid energized at 12V" and "solenoid not energized at 0V", and 2) there is no difference between the Variocam setting on a cold or a warm start. This will make diagnosis of mechanical solenoid function much easier. E.g., energize and de-energize the solenoid using a direct 12V source and see if the engine tone changes. This is of course assuming that there is no intermittent electrical break/short in the wiring from the ECU to the solenoid.

3. P1530 and P1531 means the actuator failed to move on command.

Hmm. Does the ECU use input from the Hall effect sensor to determine this, or does it use some other means?

Thanks,

Nick

[Loren]

1. I think you can find some OBD II readers that are not very good - so it is possible for them to "miss" codes.

3. Yes, the hall effect sensor and other DME readings determine faults.

[debster's man]

We have had a similar problem in our 97 Boxster - see topic "Code P1530 in 97 Boxster". Also noted the rough idling on a couple of occasions.

Our generic, auto-store-type Actron model CP9175 OBD II AutoScanner reads the codes 1530 and 1531, as well as additional codes associated with misfiring of specific cylinders.

After trying to diagnose the problem ourselves, a friendly Porsche tech scanned the codes with a Porsche diagnostic system and came up with the same diagnosis - sticking of the Variocam solenoid(s). The dealer service manager said the best thing for now is to "drive it often and drive the snot out of it". OK. The car had been in winter storage and not driven much this spring when the codes began appearing.

It continues to set the codes and I continue to erase them, although the amount of driving between codes does seem to be getting longer. The codes occur under conditions of steady-state cruising or when backing off the throttle. Our codes don't seem to correspond to the rpm thresholds stated above. When we look at the detail of the codes, they are most often between 2000 and 3000 rpm and very light load.

In our area, "driving the snot out of it" means going to redline in the lower gears and accelerating hard whenever possible. The presence of law enforcement doesn't allow for much more. Even accelerating with too much enthusiasm can attract enforcement. Have to admit, the car works better the harder you drive it.

The idea of just driving it to free up the solenoids sounds appealing but is concerning in case something worse is going on, and in case the solenoids actually do need to be replaced. So we're going with it for now and hoping for the best.

Debster's Man

[Paul Fraser]

Hi Nick, I have just been going throught the same thing with my 996: http://www.renntech.org/forums/index.php?s...c=21574&hl=

I upgraded my code reader to a Durametric to get the deeper codes (I was getting P301-303 initially from my OBD2 reader as well) and confirmed my hunch that the variocam solenoid was unserviceable. I've had two of these done on a Boxster I had and suspect you are in for one as well.

Which Scottish OPC was it you got diagnosed at? From your description it sounds like Aberdeen but £600 seems well cheap for a variocam solenoid change from them as it is supposed to be an engine out job. I paid around £450 at Ninemeister three or four years ago while visiting Warrington.

PS From what I have read our cars have an on/off solenoid; later models (post 2000?) have a hydraulically variable solenoid.