Hi,

I have some questions on (FAQ) OBD diagnostic test procedures. I'll appreciate it very much for your help in clarifying them.

Please allow me to define some acronyms first:
WOT - wide open throttle
KOEO - key on (in run position), engine off (not running)
KOER - key on, engine running


1. Procedure 3. Diag. Mode 2 sensor test, the 6th step:
"Crank the starter motor" - I take this to mean start the engine
(so this and other steps below are KOER.)

Question:
Is this correct - run test with engine running? Yes/No?

- If this is so, I would like to suggest that the procedure be revised to
clearly state 'start the engine', instead of 'crank the starter motor'.
- Also, I would like to suggest adding a step of bringing the engine to
working temperature (temp gauge needle at middle) because, see below, it
is awful to go WOT on an engine that is not fully warmed up.
- If confirmed I will email Steve to submit the suggestions.

2. Same procedure, the 9th step,
"Activate the following sensors//TPS OK in full load position":

Question:

Assuming this is KOER, how wide open should I bring the throttle to,
and for how long, for the result to be correct?

- I couldn't seem to ever get the desired code 3-3-3.
- Preferrably the answer is as specific as possible, such as '3/4 turn open and
hold for 2 seconds'.

Mcuh TIA,

Lih-Yen

Thanks to you, Bruce, Steve, and Dave.

As soon as I get a chance I will try the WOT test without the engine running and report back.

After reading your explanations I felt pretty stupid that I didn't try a different test condition (with the engine off). Perhaps I need to 'unlearn' some past experience - On a different car that I owned before, the diagnostic calls for goosing the engine (with it running), and if not open wide and long enough the OBD will repond with a code meaning 'goose harder'. I don't remember what the objectives were now, but I was always nervous doing it.

Lih-Yen

There are no OBD-I tests that involve cranking the engine without starting, so there is probably no need to get too fussy about terminology -tests can simply say "start the engine". If the engine is not in running condition and won't start then the normal test procedure is to attempt to continue cranking until the desired result is obtained (such as the LED going out to confirm the crank position sensor signal). Published test descriptions make that clear and the FAQ should too.

As for your WOT test, I would have hoped it was obvious that Volvo would never want you to keep the throttle wide open for testing with the engine running -warm engine or not, that would take it over red line.

For LH 2.4 cars at least, in test mode 2 I know that the LED should always be flashing with the throttle at both the closed idle stop position and at the full WOT position, displaying the 3-3-2 code when it clicks as you open the throttle away from the idle stop and the 3-3-1 code when it clicks as you move the throttle away from the full open position (as more or less described in the FAQ). If you don't hear the click at WOT then either the switch is gummed/faulty or the throttle plate is binding in the throttle body.

OBD table 3 in the FAQ shows fault codes for idle stop and full open throttle switch problems, so I'd expect test mode 2 in your Rex-Regina OBD system to behave as documented. However, I also notice that in OBD table 2 in the FAQ, the ignition fault codes appear to be common for the EZ-116K and your Rex-i system except for the TPS idle sense fault code (code 2-3-4 for EZ-116K, code 3-3-4 for Rex-i). So the systems are obviously different when it comes to handling the TPS switch. If you still can't get the WOT test to work as above then maybe test mode 2 in your Rex-Regina car is different and doesn't check the WOT signal. In any case, I was led to believe that the WOT signal wasn't used in our 240/740/940's -the ECU may get the signal, but the PROM didn't make use of it. However, it was supposedly used in the 850's.
--
Dave -own 940's, prev 740/240/140/120's & quasi-expert only on a good day

Very good point. In fact, the instructions are written as though one uses the diagnostic test connector to crank the starter but NOT start the engine. Far easier is just to remove the center lead to the ignition coil and complete the rest of the tests with it removed so the engine does not start. I agree: the FAQ section is confusing and I've begun rewriting it so it is more logical. All hints, suggestions welcome.
--
See the 700/900 FAQ under 'Select Link' button on the top right.

1. Procedure 3. Diag. Mode 2 sensor test, the 6th step:
"Crank the starter motor" - I take this to mean start the engine
(so this and other steps below are KOER.)

Question:
Is this correct - run test with engine running? Yes/No?

No - That's a test of the RPM sensor — presumably we'd be trying to diagnose a no-start condition. (If the engine runs, it's safe to assume the RPM sensor is OK, so the test would be pointless.)
The starter is engaged to see if RPM sender pulses are present or not.

In my opinion, the FAQ OBD description is not well organized or presented, especially the Mode 2 procedures (same for Bentley). As an overview, Mode 2 allows the following tests:

A - Fuel Related (socket 2)
1• TPS Idle contact signal OK = 3-3-2 (Manual throttle spool activation)
2• TPS WOT signal OK = 3-3-3 (Assistant operates Accellerator full pedal)
3• Speed signal from Ignition CU OK = 3-3-1 (Crank engine with starter)**
4• AC Control OK = 1-1-4 (Engine off or on???, turn AC control on)<=====???
5• AC Compressor engagement OK = 1-3-4 (Engine running, turn AC on)
6• RPM compensation, Auto Tran OK = 1-2-4 (Engine running, engage AT)

B - Ignition Related (socket 6)
1• TPS Idle contact signal OK = 3-3-4 (Manual throttle spool activation)
2• RPM Sensor signal OK = 1-4-1 (Crank engine with starter)**

** Diagnosing a no-start

The above is based on the '93 940 Regina/Rex Fuel and Ignition green book, which offers ZERO information on invoking these tests, the (parenthetic comments) above are my best guesses — with admitted confusion about Fuel test #4.


--
Bruce Young
'93 940-NA (current), 240s (one V8), 140s, 122s, since '63.