acura 1997my 25tl gst communication issue 06-2010
TRANSCRIPT
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1997 2.5TL GST Communication Issue
American Honda Motor Co., Inc.
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Summary
1997 Acura 2.5TL has experienced a generic scan tool (GST)
communication issue during smog check inspections in several states.
Honda found that 1997 2.5TL cannot initialize communication with some
tools, but can communicate with others.
Honda found that 1997 2.5 TL has a design issue on the PCM circuit(internal to the engine computer) that makes the vehicle noncompliant with
the ISO 9141 communication protocol specification. There is a diode
internal to the PCM between CPU and K-Line terminal which delays a K-
line transition from a zero to a one for up to 40 micro seconds.
Hondas investigation found that many tools cannot establish
communication with the 1997 2.5 TL because they require a switch from a
zero to a one to occur in less than 40 micro seconds as would be expected
if the vehicle complied with the ISO 9141 specification.
Because the circuitry is internal to the PCM, Honda does not have a
practical way to correct the vehicles (other than replacement of the
expensive PCM itself).
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Investigation Result
-2
0
2
4
6
8
10
12
14
16
-0.03
-0.01
0.01
0.03
0.05
0.07
0.09
0.11
[ms]
[V]
CPU Out
K-Line
96/98 ECU
CPU -+
CPU
OutK-Line
8.24us
88.76us70%
Circuit diagram
1997 2.5TL does not satisfy the communicationprotocol ISO 9141 because of a diode on the circuit
-2
0
2
4
6
8
10
12
14
16
-0.1
2
-0.1
0
-0.0
8
-0.0
6
-0.0
4
-0.0
2
0.0
0
0.0
2
[ms]
[V] CPU Out
K-Line
35.52us
59.36us
97 ECU
CPU
OutK-Line
CPU -+
70%
K-Line output delays from CPU output.
Expanded 1 bit of
Sync Byt e (0x55)
Added for an OBD II purpose
1997 2.5TL (up to 40us delay)
CPU Out
K-Line
CPU Out
K-Line
Expanded 1 bit of
Sync Byte (0x55)
Circuit diagram
1996/1998 2.5TL (normal)
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Hondas Estimated Worst Case Timing
CPUOut
K-Line
CPU -
+
The exact length of the delay time changes depends on variance
of electr ical parts and ambient temperature. Honda expects the
maximum delay time is 40 micro seconds.
96sec
70%
40sec
Circuit diagram
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Recommendations
Honda has found several tools that are tolerant of this noncompliance and willsuccessfully establish communications but not all tools can easily be modified to be
tolerant of these vehicles.
Based on the tolerance of the tool and the vehicle to vehicle variance, it is expected
that some state IM programs will only see a portion of 1997 Acura 2.5L TL vehicleswhich are problematic.
As only a limited number of PCMs are available for these older cars (and are
needed for repairs where replacement of the PCM is a necessary part of the repair),
there is insufficient inventory to replace PCMs just to correct this communicationproblem.
State IM programs that have trouble with these vehicles may need to have back-up
measures to address these cars such as 'referee' type inspection with handheld
tools found to be tolerant of this noncompliance, default to a non-OBD inspection,etc.
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Questions?
Contact:Darin Johnson, American Honda Motor Co., Inc.