Page 457 of 2189
PGM-FI System
ECM/PCM lnternal Circuit
[Fi6oil th" """n tool indicates Diagnostic Trouble code (DTc) p1607: An EcM/pcM lnternal circuit probtem.
- The MIL has been reported on.- DTC P1607 is stored.
Problern verif ication:1. Do the ECN4/PCM Reset pro-
cedure.2. Turn the ignition switch ON t).3. Wait 10 seconds.
ls DTC P 1607 indicated?
Substitule a known-good ECM/PCM and recheck. lf symptom/indication goes away, .epl.ce theorigin.l ECM/PCM.
11-188
Page 458 of 2189

[F16551l Th" ""un toot indicates Diagnostic Trouble Code (DTC) P1681: TIVA,/TMB signal line failure
Problem verification:1. Do the ECM Reset Procedure.
2. Drive the vehicle Ior several
miles at varying speeds
lnt.rmittent failure, system is OK
at ihis time. Check tor Poor con-
nections or loos€ wires at C131
llocated under right side of dash),
C438 ITCM) and ECM.
ls DTC P1655 indicated?
Check lor an oPen in the wire(TMA line):1. Turn the ignition switch OFF
2. Disconnect ECM connector C(31P)from the ECM
3. Turn the ignition switch ON (ll).
4- Measure vo ltag e between
ECM connector terminal Cg
and body ground.
Check for a short in the wire
ITMA line,:Measure voltage between TCM
22P connector terminal No 7 and
body ground.ls there battery vohage?
Ropair shod in the wire bstwe€n
the EcM (C!l) and the TcM.ls there battery voltage?
Check for an open in the wire
{TMB line}:1. Turn the ignition switch OFF
2. Reconnect ECM connector c(31P).
3. Disconnect the 22P connector
from TCM.4. Turn the ignition switch ON (ll).
5. Measure vo ltage between
TCM 22P connector termlnal
No. 6 and body ground.
Repair open in the wire between
th€ EcM {Ca) and the TcM.
Check for a 3ho.t in the wire
{TMB lin6,:Measure voltage between ECM
connector terminal C30 and bodyground,
ls there battery voltage?
Substitute a known'good ECM
and recheck. It symPtom/indica'tion goes away, teplace the origi-
nal ECM.
Reoair short in the wile b6tween
the ECM {C30} and the TCM.ls there baftery voltage?
f,epair open in the wire between
the EcM (C30) and the TcM.
IJA/T Signal (TMA/TMBI ('96 - 98 Dl6Y5 engine with GW)
ECM CONNECTOR C 131P}TMA IGRYI
fcu22PCONNECTOR
ll
TMB*{PNK}
231678910
1t'12131415161718
232a252930
Wire side oI temale
terminals
tl,
1 1-189
Page 459 of 2189
ldle Control System
System Description
The idle speed ot the engine is controlled by the ldle Air Control (lAC) Valve.The valve changes the amount of air bypassing into the intake manifold in response to electric current controlled bv theECM/PCM. When the IAC Valve is activated, the valve opens lo maintain the proper idle speed.
D16Y5, D16Y8, Br6A2 engine (M/T):
(ROTARYItac vat-vEEI{GINEcooLAI{T
VARIOUSsEI{SORS
VARIOUSSENSORS
INTAKE MANIFOTDDl6Ys {CVTl, D16Y8 engine lA/T):
D16Y7 engine:
{ROTABY)
;iy--, - ---
INTAKEMANIFOLD
11-190
Page 460 of 2189

1.After the engine starts, the lAc valve opens for a certain time. The amount of air is increased to raise the idle speed
about 150 - 300 rpm.
When the coolant temperature is tow, the IAC valve is opened to obtain the proper fast idle speed. The amount of
bypassed air is thus controlled in relation to the engine coolant temperature'
IOLE SPEED
lrpml
176
80
ENGI ECOOLANI TEMPERATURE
t" Fl
toc)
ll
't.Whentheid|espeedisoutofspeciiicationandthescantoo|doesnotindicateDiagnosticTroub|ecode(DTc)P0505
or P1508. check the following items:
. Adiust the idle speed {see page 11-220}
. Starter switch signal (see page 11-202)
. Air conditioning signal (see page l1-204)
. ALT FR signal (see Page 11-2081
' Brake switch signal (see page 11-210)
. PSP switch signal (excapt Canada model) (see page 11-212)
. A,/T gear position signal {see section 14, Dl6Y5 engine (CVT):
page 11-216). Clutch switch signal (D16Y5 engine with M/T) (see page 11-218)
. Hoses and connections
' IAC valve and its mounting O-rings
lf the above items are normal, substitute a known-good IAC valve and readjust the idle speed (see page 11-220)
|ftheid|espeedsti||cannotbeadjustedtospecification(andthescantoo|doesnotindicateDTcP0505orP]50S)
after IAC valve replacement. substitute a known-good ECM/PCM and recheck. lf symptom goes away, replace the
original ECM/PCM.
Page 461 of 2189

ldle Control System
ldle ControlSystem
lF0505 l Th" """n tool indicates Diagnostic Trouble Code (DTC) PO5O5: tdte controt system malfunction.
NOTE: lf DTC P1508 or P1509 is stored at the same time as DTC P0505, troubleshoot DTC p1508 or p1bog first. thenrecheck for DTC P0505.
Possible Cause
. IAC valve mechanical malfunction
. Throttle body clogged pon, improper adjustment. Intake manifold gasket leakage
. Intake air hose loose leakage
. Vacu um leak
. ECT sensor incorrect output
. Throttle Position sensor incorrect output*r
Troubleshooting Flowchart
The MIL has been reoorted on.DTC P0505 is stored.
Problem verification:1. Start the engine. Hold theeng;ne at 3,000 rpm with noload (jn Park or neutral) untilthe radiator fan comes on, then*r let it idle.t2. with rhe scan toot, ct'eit Ge l
Throttle position should beapprox. 10% with the throttle fully closed.E ngine coolant tempera-ture should be 194 205'F(90 96.Ci.lf they are not within thespec., repair the faulty sen
L._ _9oI9[cr]41 l3. Chec& the engine speed atidle with no-load cond;tionsiheadlights, blower fan, reardefogger, radiator fan, and airconditioner are not operating\see page l1-22O - 223).
Intermittent tailure, system is OKat this time.ls the idle speed OK?
ls it 550 rpm or less?
(To page 11,193)
*1r'96 models only
11-192
(To page ll-193)
Page 462 of 2189
I
L
1D16Y5, D16Y8 engine with M/T 81642 engine)I
D16Y7 engine:
{From page 11-192)
Check the IAC valve:Disconnect the 3P connector from
the IAC valve.
Check the IAC valve:Disconnect the 2P connectorfrom the IAC valve.
Does the engine speed drop or
the engine stall?
Adiust the {base} idle speod (see
page 11-220 - 2231.It it's impos-
aible, clean the ports in lhe throt'
tle bodv,
(From page 11-192i
Check Ior vacuum leaks:1. Turn the ignition switch OFF.2. Remove the intake air ductfrom the throttle body.
3. Start the engine and let it idle.
4. Put your finger on the lowerpon in the th.ottle body.
Ch€ck tor vecuum loaks, m.kesure the throttle valve is com_pletaly closed, end repair as nec-Does the engine speed droP?
Adiust the idle speed (see page
11-220 - 2231. lf it's impossible,
reolace the IAC velve.UPPERPORT
1 1-1 93
Page 463 of 2189

ldle Control System
ldle Air Control (lACl Vatve ('96 - 98 Dl6ys, Dl6yB engine with M/Tl
The scan tool indicates Diagnostic Trouble Code (DTC) P1508: A problem in the ldle Air Controt flAC) varvecircuit.
The IAC Valve changes the amount of air bypassing the throttle body in response to a current signal from the ECM inorder to maintain the proper idle speed.
IAC VALVE 2P CONNECTOR ICl3A)
,flrcerh-:J iYEL/BLKI
!.__-,/ -lt(v)
-T-=
Wire side of female terminals
tAcv(BLK/
ELUI
ECM CONNECTOR A I32PI
Wire side oI lemal€ terminals
VALVE
6a10ll12t3r5t6l7t8t920232a
t*25&a2A3o
The MIL hss b€on repo.ted on.DTC P'l508 i. itorod.
Problem vorification:1. Do the ECM/PCM Reset Pro-cedure,Start the engine, and warm ituP to normal operating tem-perature.
Intormittont t!llur., sy.tcm b OKat thb tim6. Chsck fol poor con-ncctionr or loo3e wirot at C138(lAC valv.l.nd ECM.
ls DTC P1508 indicated?
Check for an opcn in the wiro(lGPl line):1. Turn the ignition switch OFF.2. Disconnect the IAC valve 2Pconnector.3. Turn the ignition switch ON (ll).
4. Measure vohage between bodyground and the IAC valve 2Pconnectorterminal No. 2.
R.prir opan in the wiro botwa.nIAC valv..nd PGM-FI main r.l.y.
Chock for an opon or sho in thewire (IACV linal:1. Turn the ignition switch OFFand reconnect the IAC valveconnector.2. Disconnect the ECM connectorA (32P).
3. Turn the ignit;on switch ON (ll).4. Measure voltage betweenbody ground and ECM con-nector terminal A12.
(To page 1l-195)
11-194
Page 464 of 2189
I
I
(From page 11-194)
Repair open or short in the wirebetween ECM lAl2l and IAC
Check the IAC valve Iunction:Momentarily connect ECM con-
nector terminals A12 and A10
with a jumPer wire several times.
Does the IAC valve click?
Substitute a known-good ECM
and recheck. It symPtom/indica-tion goes away, replace the origi-
nal ECM.
Wire side of female terminals