diff --git a/src/id/precheck.a b/src/id/precheck.a
new file mode 100644
index 0000000..f7be3a6
--- /dev/null
+++ b/src/id/precheck.a
@@ -0,0 +1,42 @@
+;-------------------------------
+; PreCheckT00
+;
+; Before we trace through the drive firmware (which --
+; at least on some machines -- will loop forever looking
+; for each sector), we do a pre-check to ensure that all
+; the sectors we're about to trace are actually readable.
+;
+; Before calling this function, you need to set all 16
+; bytes of the precheck_sectors array to a positive
+; number (check that sector) or a negative number (don't
+; check that sector). The array is ordered by logical
+; sectors, regardless of the type of disk.
+;
+; If all required sectors are readable by Passport's own
+; sector read routine, this exits gracefully with all
+; flags and registered clobbered.
+;
+; If any required sector fails to read, this exits via
+; FatalError, which does not return.
+;-------------------------------
+PreCheckT00
+         lda   #$00
+         sta   gTrack
+         ldy   #$00
+@precheck_loop
+         lda   precheck_sectors,y
+         bmi   +
+         sta   gSector
+         jsr   IgnoreAddressChecksum
+         tya
+         pha
+         jsr   ReadSector
+         pla
+         tay
+         bcc   +
+         jmp   FatalError
++
+         iny
+         cpy   #$10
+         bne   @precheck_loop
+         rts
diff --git a/src/id/trace33.a b/src/id/trace33.a
index 8622849..780c74b 100755
--- a/src/id/trace33.a
+++ b/src/id/trace33.a
@@ -5,31 +5,7 @@
 ;-------------------------------
 !zone {
 TraceDOS33
-;
-; Before we trace through the drive firmware (which --
-; at least on some machines -- will loop forever looking
-; for each sector), we do a pre-check to ensure that all
-; the sectors we're about to trace are actually readable.
-;
-         lda   #$00
-         sta   gTrack
-         ldy   #$00
-@precheck_loop
-         lda   precheck_sectors,y
-         bmi   +
-         sta   gSector
-         jsr   IgnoreAddressChecksum
-         tya
-         pha
-         jsr   ReadSector
-         pla
-         tay
-         bcc   +
-         jmp   FatalError
-+
-         iny
-         cpy   #$10
-         bne   @precheck_loop
+         jsr   PreCheckT00
 ;
 ; pre-check passed, do the trace
 ;
diff --git a/src/id/trace33p.a b/src/id/trace33p.a
index e6b24c1..d0de372 100755
--- a/src/id/trace33p.a
+++ b/src/id/trace33p.a
@@ -32,6 +32,15 @@ IDSpecDel
 ; format on tracks 0-2)
 ;-------------------------------
 TraceSpecDel
+         ldx   #$0F
+         lda   #$FF
+-        sta   precheck_sectors, x
+         dex
+         bpl   -
+         inc   precheck_sectors
+         inc   precheck_sectors+7
+         jsr   PreCheckT00
+
          jsr   ClearTSBuffer
          lda   #$00       ; set a marker to see if entire
          sta   $3FFF      ; RWTS loads successfully later
diff --git a/src/passport.a b/src/passport.a
index 0d2cb93..49a865c 100755
--- a/src/passport.a
+++ b/src/passport.a
@@ -114,6 +114,7 @@ FirstMover
 
          !source "analyze.a"
          !source "id/inspect0.a"
+         !source "id/precheck.a"
          !source "id/trace.a"
          !source "id/trace33.a"
          !source "id/trace32.a"